: try trashing the preference file...
: or this could be a problem with the MML mb?
It's a Preferences problem. I think the Mk V MML specifies its own Prefs file, so it shouldn't be conflicting with the Prefs file of other AO installations, but if you ran a different (probably a newer) version of AO with Eternal, and then went back to the included version, it would give an error like that.
The solution, either way, is to delete the file "Eternal Preferences". If there is no such file, delete "Aleph One Preferences" instead.