How many breakpoints have you used in this project? Can you please post your project file?
I'm having the same problem. It's also in an interupt routine that worked two days ago. I added a external variable and now it doesn't seem to execute the interupt and I can't set a debug in the function. I've deleted all other breakpoints, so that's not the problem.
One minor thing I have learned is to turn off compiler optimizations when debugging,
I have had tools that rightly, eliminate redundant code, create jumps for that purpose to
one code snippet, but tool would not tell you a BP can no longer be set on non existent
code. I don;t think thats this problem in particular, but always worth a check.
Its a compiler setting, code optimization level. Note, however, this will not work if you
are right up against code FLASH size limitation, a problem I am now having.
A very gullible approach that has worked for me with this error message,is clearing all breakpoints(Using the menu options,not toggling them in the code window.),and setting them again.