I get the same exact error. This is the exact text as it reads in the map compiler:
Warning W072: block 0 - plane 31 too narrow!
Building fat hull ......ok
Building narrow hull......ok
Building BSP tree...
....CRITICAL ERROR.....
E701
Press any key.....
Really would like to know what I did here....
I have a city environment due in 2 weeks I am freaking out.

Shady