The original example was not incorrect, but it did still sound bad. You don't need two prepositions in a row. Would it be wrong to say "Help me off the horse?"
The original example was incorrect. To assist your Uncle Jack in his effort to dismount from his horse, one should say:
"To help your Uncle Jack off of his horse"
The salient point is not the comma but the extra preposition, "of".
It's like the overuse of "that." People use it to make statements clear even though it often results in grammatically incorrect sentences.
Edited by ShaggyZ, 27 December 2010 - 09:23 AM.