The error looks like it's trying to execute only the first line. So I guess try this:

UPDATE vb4forum.user as old LEFT JOIN vb3forum.user as new ON (old.userid = new.userid + 1) SET new.post_thanks_thanked_times = old.post_thanks_thanked_times

Okay, it's success :D kh99 you rock! Most of thanked amouths have right destination, i think i have to manual change few value.

Thank you all, both kh99 and Disasterpiece.