Anyone who has spent any considerable amount of time profiling applications must have noticed this. Your toiling away on a profile for hours, testing some password change workflow or something and suddenly AccessStudio just disappears into thin air. And at least the first time you saw this it was probably after having made numerous changes in the state machine without saving your work right? And to top it off, trying to simply re-launch AccessStudio wont help, because there are still pieces of it running somewhere in Windows voodoo land so it will complain if you attempt to run another test session. Chalk it up to yet another reason to re-boot your Windows machine.
Sorry, I have no solution, but am looking out for one. I have seen this problem in 8.0.0 and 8.0.1 so maybe the new 8.1 version will be better. I look forward to upgrading.