Unfortunately, I have some really bad news for all debugger users:
The debugger is currently broken and unusable because of recent changes in the Mono runtime. I can't give any ETA yet on how long it'll take to get it fixed since I need to do some research first. At the moment, I don't even know how to fix it, so I need to think about a solution first. Hopefully, I'll have more news after one or two days of research.
There's a Mono revision mentionend in the debugger's ChangeLog which is the last one which is guaranteed to work.