Error when creating or editing (sub)forum


I can't find the right place to post this, i hope this is the right place.

I have a little error and i can't solve it myself.

When i create a new (sub)forum or when i edit a existing one i get the error message as the attachment Schermafbeelding 2015-10-15 om 19.20.02.png . The problem is in, as far as i can see, the Tinhte Xentag addon. When i disable the addon i can create and edit the forum without any errors.

I use 1.5.1 Xenforo and 3.1.3 Xentag.

Is there anybody who could help me with this issue?