Just tried the experiment you suggested. That also failed, giving the same error.
I did shutdown all other applications, including OnlineArmor and NOD32 before installing, and then installed the rules file. At that point MBAM did open as expected.
The error comes up following a reboot to reactivate OA and NOD. THis is pure speculation, but it seems to me that this might have something to do with MBAM and OA coexisting nicely with my specific configuration. I repeat pure speculation, but the only two times I have had this problem were immediately following upgrades of OA.
PS. I am on XP Pro SP3 for the record. ;) And thinking seriously about Linux. :D