How to fix "Fatal Error: Unknown Function" bug in Call of Duty: Warzone

Call of Duty: Warzone is notorious for its issues and bugs that unfortunately dampen the experience of the battle royale.

Players are now facing yet another problem that prevents them from dropping into Verdansk. After the June 3rd update for Warzone and Modern Warfare, many players have been hit with "unknown function" fatal error.

This Fatal Error code is among many other game breaking bugs that Warzone players have dealt with in the past. Thankfully, there is a fix to this like there was to those others.

Fixing the Call of Duty: Warzone "Fatal Error: Unknown Function" bug

This issue is not just a problem for PC players. Xbox and PlayStation players from both generations of consoles are running into this problem when booting up Warzone or queuing into a game, but don't have the same fixes as PC players.

@Activision @ModernWarzone every time I try to load warzone up on my PS4 it keeps saying “error unknown function.” Just got warzone, great first impression. If anyone knows a way to fix this or knows when the bug will be fixed please tell me
— Tahmid (@Tahmid73600894) June 4, 2021

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This even includes private matches. The error crashes the entire game, stopping users from playing any part of Call of Duty: Warzone. Players have reported that single player on Modern Warfare is still working, however.

@ATVIAssist @RavenSoftware when I go into a private/practice match on warzone or mw multi-player, and try to play a BR practice game or a MP custom game. It kicks me to the start with an error, (unknown function). I'm on Xbox series x. pic.twitter.com/qSISrODGur
— Ryan Freese (@freese_ryan) June 4, 2021

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At this point, contacting Activision support seems to be the only tried and true method to solve the error. Other solutions have come out, but they may not work for each user.

Solution 1 requires Warzone players to open Battle.net, select Warzone, click on Options, and select Game Settings. Select "additional command line arguments" and type -D3D11 in the box. Click done and launch Warzone.

Solution 2 involves opening My Computer on the PC. From there, open Documents and then Call of Duty: Modern Warfare. Delete the folder labeled players and try to launch Warzone.

@ATVIAssist having issues. Just downloaded the game on my pc, and you have to do the tutorial before playing warzone. My game has a "fatal error, unknown function" during the loading screen to the tutorial. It freezes then has that error. I'm stuck. Let me know what you think.
— Dylan (@Dylan44619968) June 4, 2021

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Solution 3 has players opening Battle.net, going into the COD: Warzone options, and clicking Show in Explorer. Open the MW folder and delete all files except "data." Open options, select Scan and Repair, then launch the battle royale.

Last up is Solution 4. Open the PC's Control Panel from the Start Menu. Search for System, select it and choose Advanced Options. Locate the Advanced tab and click Settings in the Performance section. Again, go to the Advanced tab.

Click Change under the section labeled Virtual Memory. Uncheck the box for "Automatically manage paging file size for all drivers" and select "No paging file" underneath it.

Press the Set button and click yes. Press okay after that, then close the Control Panel and restart the PC. When it boots back up, open Battle.net and launch Warzone.

All of these fixes were determined by YouTuber TECH SITES. He details all of the fixes and how to reach each solution. The video also notes how to revert any of these changes for Warzone if they don't work.