This could be related to a possible bug I was about to post.
I've found that for at least the last few days (and possibly longer, as I was a little lax about updating - maybe as much as a few weeks), Mafia doesn't seem to be closing properly. By that I mean a javaw.exe process is left running when I close Mafia down, which did not happen in the past. (I do not have another Java app running, as far as I am aware).
While this orphaned javaw process is running, Mafia silently fails to start. If I kill it, Mafia starts normally.
I have specifically noticed this issue with r9984, and I believe I have seen it with r10005.
I'm hesitant to state with certainty that it is a Mafia problem, as it could certainly be something specific to my system, and I have done very little in the way of investigation (particularly as there is an easy workaround). But I figured it was worth asking if there has been a Mafia change that could conceivably cause such behaviour.
And my issue would seem to match the symptoms described in the OP, though far from conclusively.