Originally Posted by
duckbillplatty
In earlier releases of vBulletin, there was a mechanism that only allowed a certain number of "reputations" per post. The numbers aren't exact, but it was something along the lines of this: If you have only 3 posts in 6 months, then you are only allowed to gives 2x's that number of "reputations", so 6. After that, the system assumes you are "spamming" or misusing the reputation system. I don't know if vBulletin still behaves this way.
Also, be sure that you are trying to add reputation points to the same user repeatedly since that would flag you in the software as well.
Just remember, the reputation system is near meaningless. No administrator or moderator would care enough about it to change anything like that for a particular user. If it's not working, then it is most likely to be because of some part of the software preventing behavior that could indicate an exploit of the system.