I did this too! I set up a notification to shutdown the computer if my pump RPM goes below a threshold value. I had something set up wrong and got into the same situation. The computer would shut down as soon as the Aquasuite service started. I got out of it by booting into safe mode and loading a recent Windows restore point. I posted about it
HERE. Another forum member responded that he did the same. He fixed it by booting into safe mode and editing the config XML file, as Stephan suggested. So you are not the first to have this happen. I guess the Playground has the potential to get you into trouble, because its a fundamentally powerful tool. Some sort of "safety" or escape mechanism would be nice to have, so long as it is configurable and will not end up being an impediment in some cases.