I installed OC 9.1 from scratch and completely new. At the last page of wizard I entered the admin name & password, the same user name for mysql, the root password for mysql, database i named it owncloud and localhost. After pressing finishing installation I received the following error message: SQlSTATE[28000] [1045] acccess denied for user@localhost (using password ; YES)
you can't choose an username and then use the root password for mysql (how should that work?). Instead make sure that no databases and users from an old oC installation exists and specify the root user and the root password in the database fields as described in the installation documentation at doc.owncloud.org