Crash Due To Vertex Buffer? o.O

Whenever i start Cs_miltia i can play for a bit but then i get this error

http://s866.photobucket.com/albums/ab229/Routertrout/?action=view&current=Untitled-1.jpg

if you cant see that the error is “Failed to lock vertex buffer in CMeshDX8::LockVertexBuffer”
any help would be good ive tried doing -dxlevel 95and all that but still does the same and my graphics card is up to date

anyone got any ideas?

-bump- needs help