Zeneticus - you haven't said whether you are using the 'give gift' button (the little wrapped present) or just offering cash and clicking 'make offer'. If it's the latter, you aren't actually offering the money as a gift, you're offering the cash in exchange for whatever the Pope can give you that he thinks is worth the amount of money you're throwing at him. If he can't think of anything suitable he'll turn it down.

On several games on VH/VH I have yet to have the pope refuse a gift except when I am excommunicated, and even then a suitably large gift can help.