Hi, Whillie2000,
The grammatical rule which is broken is this:
After a preposition, the
-ing form of the verb, not the infinitive, must be used (if a verb follows).
The preposition is
of. The verb is
be. (The intervening "him" does not change the rule.)
"... afraid
of him be
ing ..."
I hope that clears it up!
CJ