User cannot create repeating events

I have a user with an issue of not being able to create repeating events on another user’s calander. Its typical for other users to be able to share this in the organization I help administrate, and multiple users have the same access is this user.

Basically user X needs to have access to user Y’s calander and I ensured that user X is listed under “Access & Deligation” for user Y’s mailbox preferences. Could this possibly be an ACL issue? If so what specifics should I look for to ensure full calander access?