At the top of the thread, you said you were using OCC 5.2 and VC++ 6.0, but now in your signature I see you're using OCC 6.1. Are you using the standard installed DLLs? If so, consider that it was compiled with VC++ 7.1 and uses the corresponding runtime libs.
Have you tried recompiling all the OCC sources from scratch with VC++ 6.0, the dsw workspaces are in the ros/adm/win32 folder and the instructions for building them are in the documentation. Well worth a try, but it'll take some hours to complete (build the debug libs as well, but ignore DRAW unless you've got a tcl/tk distro - and you won't need WOK much either).

Pete