FYI to others that may also be experiencing issues.
Donnelaith's trouble was related to the ThorUI AU application being installed in the EverQuest II\UI\thorui directory.
Note: When you install the AU, you should allow it to install to the default location of C:\Program Files\thorui unless you have a good reason to move it. It will work in other locations just shouldn't ever go in the directory where the actual ui files go.
If this is your issue as well simply uninstall and then reinstall to the default location.