"There is no source code available for the current location"

I'm using Visual C++ Express Edition.In debugging mode,After I edited code,I exited debugging mode and debuged file again..It informs that "There is no source code available for the current location" and two button options," OK and Show Disassembly"....I can't debug file where I set breakpoint..what the error is ?..How to fix it?please help me!!!Thanks very much.....

Is this unmanaged C++ or Managed C++?

If the latter, check if Unmanaged Code Debugging in Project->Properties->Configuration Properties->Debugging is off. It has to be off.

If the former, turn it on.

Rebuild all after doing it.

I don't see "Unmanaged Code Debugging" in this part...please help me....