There's no way of knowing, but I suspect the author of the add-on would know.
There are several fields within XF tables that have a 25 character limit. Of course with it being an add-on it's possible the field actually belongs to a field added by the add-on to one of our tables or a field within a table the add-on has added.
Old topic I know, but for reference to others (as my googling for this error lead me straight here) I had identical problem. It was within addon*.xml and I'd blown out the permission field interface_group_id but as Chris D says there are probably a few others to check as well.