Have you update it to the current version we uploaded yesterday ? It's 2.7.0.17, it will be downloaded if you install any scenery, or if you run the Stand-alone Addon Manager.
Note that, if you (for testing purposes), keep launching, exiting and restarting FSX many times in a row, it's best to allow some time before each try, not much, but at least 15-20 seconds, to allow all loaded modules, memory and handles to be released, otherwise you'll increase the chance of those kind of troubles. This is especially true for external .EXE loaded in the EXE.XML because, they might be confused by an FSX exiting and loading again too fast, and be stuck on the task manager.