I'm guessing you might have recently travelled somewhere? Your problem has been reported when people travel at the end of their day, and end up with a negative case number. They usually start out the next day with a lesser number of cases, to make up for the ones that were used in extra the previous day (ie. -- tomorrow, you'll have 11 cases instead of 12).
The Locker Ghost is a separate issue, and has to do with being impatient when the server is slow. (People will hit buttons too many times while the server is chewing on something, and Bob's yer Uncle, Ghostie's suddenly cleaned out something from the Locker, or added to it. It's not fun when you lose 3 or 4 AVH items. Trust me, I know. :-)
Hope that might help a bit for an explanation? Good luck!!