To troubleshoot this issue, verify the following: 1) The database is online. 2) The database is not in a restoring state. ...

To troubleshoot this issue, verify the following:
1) The database is online.
2) The database is not in a restoring state.
3) The database has not been deleted.
4) The database is accessible.
5) If the database was part of a mirroring session, either re-establish mirroring between the partner SQL Server databases or remove the database from protection and recreate the protection group for this database.