Having troubles with PrisonRankup plugin

Hello. I've been trying to set up a prison server and I've got everything figured out and set up... except for the fact that every time someone tries to rankup I get "An internal error occurred while attempting to perform this command". If anyone could help me out that would be great. If you need extra information about it tell me and I'll give you it.

Meh, is anyone planning on helping me? ;-;

EDIT by Moderator: merged posts, please use the edit button instead of double posting.