[@mercime Participant 14 years, 2 months ago]

=== Upgraded to 3.0.4, re-enabled multisite, now i have a problem. If I turn off multisite the forum works just fine. Once I turn it on ===

You do not need to nor should you “disable” then “re-enable multisite” to upgrade your multisite installation. Have you tried to re-run forum installation I mentioned in previous post?