Read Only Mode

We have changed DB Access Method from AD-integrated to MSSQL Authentication.
Now nobody can change any entry or create new ones. The whole Administration Tab is greyed out. It seems, we are in read only mode. DB User is db_owner of the RDM DB. We have also tried to do a rollback and use AD-Authentication, but it doesn't work neither. Any hint, how we can switch back to normal mode?
edited by Flotto on 11/10/2014