Are you using v9 or greater of Snag-it? (I may be off on the version level)
If so, customize the function keys in Snag-it. They added a couple of new ones that capture video. What seems to be happening is that Snag-it captures the F21 key and thinks you want to start a Snag-it video recording. Change the key combo to something that you are not likely to need (or to nothing if you don’t want record video that way).
At least at a past employer we found the issue w/ Snag-it. There may be other tools that do something similar with to capture the key instead of letting your emulator have it.
Took us about 2 years to figure that one out. We asked IBM they had no clue and nearly a year later they called and indicated that they found it had something to do with snag-it but were not sure exactly what. But then I has something that I could work from and we started to piece the puzzle together and determined it was only users w/ newer rollouts that had the newer version of Snag-it. HTH.