Crashes After CSG Sub

[Emulsion]

hey guys i have this problem in UDK where i can take a simple flooring (4000:x 4000:y 100:z) and i bring out a Static mesh for (ie-Pillar) And i do a CSG Subtract on the floor and it crashes. Any idea's on waht this could be?

Thanks in Advance,
Emulsion

[Emulsion]

*Bump*