Fix for Player Login Crash Bug
UT General :: Jul-16-03
From UnrealAdmin.org, here is a fix for the player login crash bug. This will be incorporated into the next patch as well: 

All admins are advised to open their Core.int files and modify the following entry:

LoadClassMismatch=%s is not a child class of %s.%s 

Change it to read: 

LoadClassMismatch=%s is not a child class of %s. 

This will prevent malicious clients from crashing your server by specifying an invalid player class when logging in. This fix should only be applied to Unreal Tournament servers, and you should restart your server after modifying the Core.int file in order to apply the changes.