bsp to static force closes

having a bit of an issue, everytime i complete a prop using the primative bsp brushes it force closes unreal engine, normally right after i hit enter for the new static meshes name ? any ideas or anyone else having this issue, also heard using bsp brushes was a bad idea for performance, is this still an issue if they have been converted to static meshes ? thanks in advance for any info.

sorry meant to throw this one under content creation, going a little to fast this morning for the brain power i have available to me.