I'm using CVI 7.0. I have just added a new callback of a .uir button. I compile the code in debug mode. After entering the code under tscvirun, I am not able to place a breakpoint in the new code, and I get the message I posted above.
Depending on what kind of edits you're doing, it seems like sometimes the debugger gets out of sync with the editor. Try recompiling and saving your file. If tscvirun is calling a project of which the file in question is only a part, try rebuilding the project. You could also try adding a blank line to the file, then save it and recompile it.