ACE adds files to the Logs folder with the file name like:

[ACE] - SERVER-NAME_YYYY.MM.DD.HH.MM.SS_MAP-NAME_PLAYER-NAME.log

If you open that file in a text editor like notepad it should explain why someone got kicked.  

If it's a mod then you will see that in the &quot;Call Graph&quot; section.  You can add the package name to your UnrealTournament.ini under &quot;ACEv08g_S.ACEActor&quot; as &quot;UPackages[X]=&quot;.  Where X is the index number (0, 1, 2, 3 etc...).

It may also be a custom graphics device (OpenGL, D3DX9 etc).  The white list for this is defined in the ACE.defs file in your System folder.  This file should be updated automatically but you can get a current copy of that file at http://utgl.unrealadmin.org/ACE/20120426_A/ACE.defs