Heap Corruption with a popup that prevents the batch file from restarting the process because it doesn't fully crash out (main stream keeps running). Kanras and I have spent days worth of time working on going through code from the time it started happening (September - November 2011) checking and rolling back code and haven't found the cause.
Frankly at this point it is the single biggest thing pissing me off, more so than even the latest drama troll scandal.
http://www.rogean.com/images/worldcrash.png
When this happens it just starts spamming connection fails because the UDP Thread of the process is no longer executing, which is also the reason it stops responding to any UDP packets from clients for logging in or zoning.