Why does the KF2 SDK crash at startup?

According to the guide author, it starts crashing once you have fully loaded too many package folders. Load folders one at a time or unload content before closing the SDK.

How do I completely reset the KF2 SDK?

Delete local content for Killing Floor 2 SDK in Steam Tools, delete the hidden KillingFloor2 folder in AppData\Local\Temp, then start the SDK again.

Does the SDK need to be on the same drive as the game?

A commenter reported that installing the SDK in the same location as the game fixed a SDK that refused to run.

Fixes & Performance

KF2 SDK Crashes on Startup: Causes and Clean Reinstall

The Killing Floor 2 SDK (the Unreal-based editor in Steam Tools) is known to crash on launch. This page collects the causes and fixes from a community guide, plus extra solutions from its comments. If you are new to the SDK, start with the SDK mapping guide.

Why it crashes

In the author's experience the SDK starts crashing on launch after you have "fully loaded" too many folders in the Content Browser. The only prevention is to fully load one folder at a time, or to unload content before you exit the SDK.

Troubleshooting steps

These can be done in any order:

Verify both caches (the game and the SDK) in Steam.
Uninstall and reinstall the SDK.
Unplug external storage devices before starting the SDK.
Always delete the logs in Documents > My Games > KillingFloor2 > KFGame.
When the BugSplat window appears, open "View Report Details". It shows exactly what caused the crash and where.

The full clean reinstall

If nothing above helped, wipe the SDK completely:

In Steam, open Library > Tools > Killing Floor 2 SDK and choose "Delete local content".
Delete the folder KillingFloor2 in AppData\Local\Temp. The folder is hidden. Type %appdata% into the Windows search bar, which opens AppData\Roaming, then go up one level to AppData\Local.
Start the SDK. It will behave like a first launch.

Fixes from the comments

Install the SDK in the same library location as the game itself.
If you are on a beta branch of KF2, leave the beta. One commenter said this alone fixed it, and another asked whether the beta review branch was the cause.
Another user fixed it by renaming Documents\My Games\KillingFloor2 to KillingFloor2.old and then running KFGame.exe (in killingfloor2\Binaries\Win64) as administrator. The game rebuilt a fresh KillingFloor2 folder.
If the game then crashes after a few minutes of play (reported on Windows 8.1), set KFGame.exe to run in Windows 7 compatibility mode via Properties > Compatibility.

The original discussion came from the Tripwire forums thread about the SDK crashing on startup.

FAQ

Why does the KF2 SDK crash at startup?: According to the guide author, it starts crashing once you have fully loaded too many package folders. Load folders one at a time or unload content before closing the SDK.
How do I completely reset the KF2 SDK?: Delete local content for Killing Floor 2 SDK in Steam Tools, delete the hidden KillingFloor2 folder in AppData\Local\Temp, then start the SDK again.
Does the SDK need to be on the same drive as the game?: A commenter reported that installing the SDK in the same location as the game fixed a SDK that refused to run.