System error after debugging multithreaded applications

After debugging a multithreaded application, I have error of the system library 'ntdll.dll'. Error code is 0x4000001f (STATUS_WX86_BREAKPOINT). Error occurs on a case by case, and only when debugging via the Delphi IDE. I use Delphi 2010 on Win7 x64. In what may be problem? Thanks.

I have witnessed this occur on only one computer, though we never did discover EXACTLY what caused it. The error occured with ANY multithreaded application attached to the debugger (no matter what the threads were doing). In the end we reformatted and reinstalled the machine, the problem disappeared. I'm not suggesting you SHOULD format and reinstall, but... if all else fails!