Revealing mistake: We can see Ecliptor's zipper from behind - slightly revealing on Saban's part, considering Ecliptor is supposed to be an evil monster henchman of Astromena's.
Crystal Blue Persuasion - S3-E15
Factual error: When Frank, Olga and he rest of the Back Step Team meet Commander (a Navy O-5 Rank) William Streck, he is dressed in a U.S. Air Force Uniform with the rank of Colonel (O-6).
The Origin of the Silver Surfer: Part 1 - S1-E1
Other mistake: When the citizens of Zenn-La are shown from the back listening to Uatu warning them of the coming of Galactus, none of them budge in the slightest.