We’ve been getting an ass load of customers with random and strange server crashes. Apparently SMP is living up to its alpha status and crashes a lot.
Check out this thread for more information: http://arstechnica.com/civis/viewtopic.php?f=22&t=1116264&start=3880
As soon as a fix comes out, we’ll install it and make an update available in the panel – until then, you can try re-making a world or reinstalling… but it looks like we have a buggy SMP for now.
UPDATE: Notch released a small update that may or may not have fixes in it. Either way, it has been installed and servers are now flagged for upgrading. Go get it! Cross your fingers and remember to back up your world data in the hgsbackup folder before your upgrade/reinstall.
UPDATE 2: This was part of our epic failure: http://status.hostedgameservers.com/2010/oh-man-we-messed-up-big-with-minecraft