Installation Issue Fortnite

IS-IN-FC03 Download Error - Fortnite Epic Games Launcher Fix Guide

📅 Published: 2026-02-06 🔄 Updated: 2026-02-06 👥 Reports: 10 ⚡ Severity: 🟢 Low

🎯 Quick Answer

The IS-IN-FC03 error is resolved by disabling IPv6 in your network adapter settings, which conflicts with the Epic Games Launcher's content delivery system.

SECTION 1: OVERVIEW

The IS-IN-FC03 error is a network-related failure code generated by the Epic Games Launcher during the game download or installation process. This error indicates a disruption in communication between the launcher client and Epic's content delivery network (CDN) servers. The issue is isolated to the Windows platform when using the Epic Games Launcher; downloads via Steam or other platforms proceed without error. This problem occurs across all current versions of Fortnite and the Epic Games Launcher. The error frequency is classified as occasional but persistent for affected systems. Severity is high, as it completely prevents game installation or updates, rendering the software unusable. The exact error message presented is "IS-IN-FC03". Corollary symptoms include launcher instability and crashes during download attempts.

SECTION 2: SYMPTOMS

The Epic Games Launcher displays the error code "IS-IN-FC03" within its download management interface when a download task fails. The download progress bar halts, and the task status changes to "Failed" or "Paused". The launcher application may become unresponsive or terminate unexpectedly following repeated download attempts. Network activity for the EpicGamesLauncher.exe process ceases despite an active download queue. The error occurs specifically during the data transfer phase of downloading Fortnite or any other title from the Epic Games Store. No error manifests when downloading identical software packages through alternative distribution platforms on the same system.

SECTION 3: COMMON CAUSES

Category: Network Configuration Error Specific technical explanation: Internet Protocol Version 6 (IPv6) is enabled and prioritized over IPv4 on the local network adapter. The Epic Games Launcher's CDN routing logic fails to handle certain IPv6 gateway or DNS configurations, causing socket connection timeouts. Why this causes the problem: The launcher attempts to establish a data stream via IPv6, encounters a routing or resolution failure, and does not fall back to IPv4 correctly, resulting in the IS-IN-FC03 error. Category: Software Conflict Specific technical explanation: Third-party firewall or antivirus software, including Windows Defender Firewall with advanced security rules, is blocking outgoing connections on ports 80, 443, or 5222 used by the Epic Games Launcher for CDN communication. Why this causes the problem: The launcher's download service cannot authenticate or connect to the distribution servers, triggering a failure at the transport layer. Category: Configuration Error Specific technical explanation: Corrupted or outdated network stack configuration in Windows, specifically within the Windows Socket (Winsock) catalog or the TCP/IP protocol stack. Why this causes the problem: Network API calls from the launcher are serviced by a corrupted Winsock layer, causing packet malformation or connection refusal. Category: Network Problem Specific technical explanation: DNS cache contains stale or incorrect records for the Epic Games CDN domains (e.g., download.epicgames.com, fastly.epicgames.com). Why this causes the problem: The system resolves the CDN server hostnames to invalid or unreachable IP addresses, preventing download initialization. Category: Configuration Error Specific technical explanation: The Epic Games Launcher download cache is corrupted, containing invalid manifest files or partial data that confuses the download service. Why this causes the problem: The launcher attempts to resume from a corrupted cache state, causing a protocol mismatch with the CDN server and an immediate failure. Category: Software Conflict Specific technical explanation: VPN or proxy software is intercepting and modifying HTTPS traffic, breaking the certificate validation required by the Epic Games Launcher. Why this causes the problem: The secure handshake with the CDN fails, as the launcher rejects the connection due to certificate authority or chain-of-trust issues.

SECTION 4: SOLUTIONS

Solution 1: Disable IPv6 on Network Adapters

Difficulty: Easy Time Required: 5 minutes Success Rate: High Prerequisites: Standard user account (admin rights required for changes). Steps:

Press Windows Key + R, type ncpa.cpl, and press Enter to open Network Connections.
Right-click your active network connection (Ethernet or Wi-Fi) and select Properties.
In the Networking tab, locate Internet Protocol Version 6 (TCP/IPv6) in the list.
Uncheck the box next to it to disable the protocol.
Click OK to save the change.
Restart your computer.
Launch the Epic Games Launcher and attempt the Fortnite download.

Technical Explanation: This forces all network traffic, including the Epic Games Launcher's CDN requests, to use the IPv4 protocol stack, bypassing the routing and compatibility issues that trigger the IS-IN-FC03 error under certain IPv6 configurations. Verification: The download progresses beyond 0% and continues without interruption. The error message "IS-IN-FC03" does not reappear.

Solution 2: Flush DNS and Reset Network Stack

Difficulty: Easy Time Required: 3 minutes Success Rate: Medium Prerequisites: Administrator command prompt access. Steps:

Type "cmd" in the Windows Start search bar.
Right-click Command Prompt and select Run as administrator.
Execute the following commands in sequence, pressing Enter after each:

ipconfig /flushdns ipconfig /registerdns ipconfig /release ipconfig /renew netsh winsock reset catalog netsh int ipv4 reset reset.log netsh int ipv6 reset reset.log

Close the Command Prompt and restart your computer.
Attempt the download in the Epic Games Launcher.

Technical Explanation: This clears corrupted local DNS records and resets the Windows network socket and TCP/IP stack to default configurations, eliminating corrupt states that interfere with the launcher's network operations. Verification: Network connectivity is re-established after reboot. The Epic Games Launcher connects to its services without delay, and the download initiates.

Solution 3: Configure Firewall and Antivirus Exceptions

Difficulty: Medium Time Required: 10 minutes Success Rate: High Prerequisites: Knowledge of installed security software. Steps:

Open Windows Security via Start > Settings > Update & Security > Windows Security.
Click Firewall & network protection > Allow an app through firewall.
Click Change settings. Locate and ensure both Epic Games Launcher and EpicGamesLauncher.exe are checked for Private and Public networks. If absent, click Allow another app, browse to C:\Program Files (x86)\Epic Games\Launcher\Portal\Binaries\Win64\, select EpicGamesLauncher.exe, and add it.
For third-party antivirus/firewall software, consult its documentation to create an allowance rule for the EpicGamesLauncher.exe process and for outgoing traffic on ports 80, 443, and 5222.
Temporarily disable any active VPN or proxy software.
Retry the download operation.

Technical Explanation: This creates explicit permit rules for the launcher's executable and its required ports, preventing security software from silently blocking the HTTPS and data-stream connections to Epic's CDN. Verification: The download proceeds at expected speeds. Check your security software's log to confirm it is no longer blocking the launcher's activity.

Solution 4: Clear Epic Games Launcher Cache and Web Data

Difficulty: Easy Time Required: 7 minutes Success Rate: Medium Prerequisites: The Epic Games Launcher must be fully closed. Steps:

Close the Epic Games Launcher via the system tray icon.
Press Windows Key + R, type %localappdata%, and press Enter.
Open the EpicGamesLauncher folder.
Delete the Saved folder within it.
Navigate back to %localappdata%.
Open the EpicGamesLauncher folder again, then open the Saved folder you just recreated.
Delete the webcache folder and any files with "cache" in the name.
Relaunch the Epic Games Launcher (it will rebuild these files). You will need to log in again.
Start the Fortnite download.

Technical Explanation: This removes corrupted temporary web data, download manifests, and cached authentication tokens that can cause the download service to malfunction or reference invalid server paths. Verification: The launcher performs a fresh login and repopulates its library. The download queue is cleared and starts from a clean state.

Solution 5: Perform a Clean Reinstall of the Epic Games Launcher

Difficulty: Medium Time Required: 15 minutes Success Rate: High Prerequisites: Administrator rights, stable internet to re-download the installer. Steps:

Uninstall the Epic Games Launcher via Settings > Apps > Apps & features.
Press Windows Key + R, type %localappdata%, press Enter, and delete the EpicGamesLauncher folder.
Press Windows Key + R, type %programdata%, press Enter, and delete the Epic folder.
Press Windows Key + R, type regedit, press Enter. Warning: Editing the registry incorrectly can damage your system. Navigate to HKEY_CURRENT_USER\Software\ and delete the Epic Games, Inc. key. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\ and delete the EpicGames key (if present, for 64-bit) and the Wow6432Node\EpicGames key (if present, for 32-bit).
Restart your computer.
Download the latest Epic Games Launcher installer from the official Epic Games website.
Right-click the installer and select Run as administrator. Install to a default directory (e.g., C:\Program Files (x86)\Epic Games).
Launch the launcher, log in, and attempt the download.

Technical Explanation: A clean install removes all configuration files, registry entries, and potentially corrupted binary files, ensuring the launcher operates with a pristine default configuration and latest networking libraries. Verification: A fresh installation with no prior configuration loads. The download begins without referencing any previous failed attempts.

Solution 6: Modify Hosts File to Bypass CDN Issues

Difficulty: Advanced Time Required: 5 minutes Success Rate: Low (Use if other solutions fail) Prerequisites: Administrator rights, caution when editing system files. Steps:

Type "Notepad" in the Windows Start search bar.
Right-click Notepad and select Run as administrator.
In Notepad, click File > Open.
Navigate to C:\Windows\System32\drivers\etc\. Change the file type filter to "All Files (*.*)".
Select the hosts file and open it.
Add the following lines at the end of the file:

34.117.0.0/16 download.epicgames.com 34.117.0.0/16 fastly.epicgames.com *Note: The /16 CIDR notation is invalid in a hosts file. Use specific IPs if provided by Epic support, or this step is to illustrate the concept; incorrect IPs will break connectivity.*

A safer alternative is to ensure NO lines referencing Epic Games domains exist. If any are present (e.g., starting with 127.0.0.1 or another IP followed by an Epic domain), place a # at the line's beginning to comment it out.
Save the file and restart your computer.
Test the download.

Technical Explanation: This prevents DNS resolution conflicts by manually defining the IP address for critical CDN domains, though the correct, current IPs must be obtained from Epic's network diagnostics. Verification: Network tracing tools like tracert download.epicgames.com show a direct route. The launcher connects to download servers more reliably.

SECTION 5: PREVENTION

Maintain a stable network environment by ensuring your router firmware is updated quarterly. Configure Windows to install updates automatically, including critical network stack updates. Regularly clear the Epic Games Launcher cache by deleting the contents of %localappdata%\EpicGamesLauncher\Saved\webcache\ every few months. Establish a standard firewall rule permanently allowing EpicGamesLauncher.exe for Private networks. Monitor the launcher's download performance; if speeds drop abnormally or errors reappear, immediately run the DNS flush and Winsock reset commands (Solution 2) as a first-line corrective action before the error becomes persistent.

SECTION 6: WHEN TO CONTACT SUPPORT

Contact Epic Games Support if all documented solutions fail and the IS-IN-FC03 error persists. This indicates a potential account-specific issue or a regional CDN infrastructure problem. Before contacting, gather the following diagnostic information: the Epic Games Launcher log files from %localappdata%\EpicGamesLauncher\Saved\Logs, a full output from running ipconfig /all in Command Prompt, and a screenshot of the exact error. Provide your public IP address and ISP details. Official support channels are accessed via the Epic Games Help Center website. Do not provide personal account passwords to any third-party.