This issue has plagued MCNR since day 1. If it happens again you need to type /showeventlog and paste the chat log here please.
I've seen some reports of players' games crashing when entering the bank. I have no idea why that would be, or if it's related.
Unfortunately this is a tough one to solve (black screen and also players timing out when entering the bank) as I cannot replicate it.
If anyone can repeatedly replicate either of these bugs, let me know.