Today, at work, I managed to wrangle Windows XP into thinking there was an instance of our in house, single instance, application running when actually it wasn't. Not sure how I did it. Just happened after lots of impatient debugging and process killing but anyway...
Every time I clicked the .exe I got this error message: "An unexpected error has occurred because an operating system resource required for single instance startup cannot be acquired" Boooo. So I Googled it - standard. And I found this page on msdn.
http://msdn.microsoft.com/en-us/library/ms184509(classic).aspx
I'm really not a big fan of Microsoft bashing but I did enjoy their troubleshooting guide:
Steps 1 & 2 I liked. Alot. Mostly because I didn't have to do anything and I'm so lazy.
Steps 3 & 4 are the belters. I was tempted to ring them. If only I wasn't so lazy...