If a man had a problem with a girl's intelligent, it would probably be indicative of his insecurity more then anything...
However, intelligence can sometimes be intimidating because the said intimidated person may not no what the fuck the said intelligent person is going on about! Feeling stupid is not a good feeling = thus leading to intimidating.
An attractive intelligent person is a double whammy because beauty on its own can be quite intimidating to some people, combined with intelligence would be quite frightening.
Beauty and brains are qualities that a large majority of the population strive for.