I expect one of your primary ClassAct/ReAction classes got clobbered by an older version. This was also a common occurrence when installing certain versions of AWeb. I can't remember exactly which library it is, but if you search the forums it should turn up. Restore the library from backup (or the 3.9 CD or BB2 or wherever) and you should be good to go!
i seem to recall imagefx installs overwriting picture.datatype or some such..might be my bad memory
i think you are right about the classes.
