Are all the proper files uploaded?
See I wonder if you have vbulletin 3.6.12 why that code would be called at all. The code is here in header-inc.php
Content visible to verified customers only.
Basically its a conditional that states if its defined which it would be in vbulletin and it is equal to or greater than 400 that it do things the vb4 way not vb3.
Something is fishy there. If you upgrade your vb
to 3.86 what happens?