Theresa,
It sounds as if you have a corrupt VI and or corrupt control. The solution or fix for this would be to identify the corrupt control, delete it, and create a new one. This usually cleans up those .cpp drawing errors. The tricky part is finding the problematic control. Do you know when this started to happen? Would you be able to link this to an individual control or function on the block diagram.
If the VI is corrupt...you can try copying the whole block diagram to a new VI...and the FP as well. Of course, this can be more difficult with larger VIs.
hope this helps,
-Brett