well all I did was a variation on Kirby's idea so maybe something the same on 2.5 vbgallery
In the user_merge plugin of vbgallery is this and all I did was add what is in bold
Content visible to verified customers only.
I then edited the adv_gal_member_block and adv_gal_member_stats template and replace the lastpostid to gallastpostid
I can only assume that you added a new plugin that was hooked to vbulletin not vbgallery with some new hook line that had vbgallery stuff and since it did not also contain the join statement against the ppgal_user table thats why you had an error.