It's a CPU exception that is catched by Windows and passed on to LabVIEW. After such violations of the process environment it is generally not possible to cleanly recover and continue work as the program only knows that something went wrong when the CPU tried to execute the program code, but not what, where and when exactly.
This kind of errors is often caused by calling external code in DLLs but there is also a possibility that your VI got corrupted somehow. The solution, if such errors suddenly occur, is to revert to a clean version of the software in a proper version control repository. You are using something like SubVersion or GIT, aren't you? If not, it would be a very good time to start with that now!