He's using ZHLT (I'm such a newb basher I helped him set it up yesterday), I'm guessing you have no problems with Batch Compiler.
Check the
mapname.log or mapname.err[/b] files (same folder as teh .map file).
You did Export To Map and compile that right? Of course you did
Well, check those error and log files, and post them up here, if you see the word
LEAK you rememebr how to find them?
Fly around outside the map and look for gaps, preferably in 3d flat textured in teh camera screen.