I don't think I've seen this one in a while. I see you're running v10 - is that 10.5 Pro? It might help to know the version of Windows and the version of Office you're using. Have these changed recently? Are you in a position to upgrade to v11.3, which uses the ADE Access Database Engine instead of Jet?
One other thing to check would be the timing of any script that runs Monarch - perhaps there are lots of projects being run at once which are causing the issue?