Can i go back from a new version to an old version?

[Daja]

I've upgrade it my forum to a new version of vbulletin but most of features like skins etc etc dont work properly, now i'm trying (install) to go back to 3.6.5 but i cant for some reasent, now if i try to delite any of the posts it comes up data base error, i have to try 3-4 times before it can b delite it.
Can some one help me plz.

[Opserty]

I don't think there is any supported/recommended way to downgrade vBulletin. You'll have to restore a backup of the database from before the upgrade and the restore the files from the previous version you had installed before the upgrade (3.6.5)