Database '%.*s' is already open and can only have one user at a time.
This error occurs when trying to access a database that is already in use by another user or session. SQL Server detected an attempt to access a database that is in single-user mode.
Verify that the database in question is actually in single-user mode. Do this by executing the following Transact-SQL statement:
sp_helpdb database go
If the database is truly in single-user mode, the status result column will list single user as the access mode.
To see what login is accessing the database, you can execute an sp_who system procedure and scan the database name result column for the specified database.
If single-user mode privilege is a problem, you might need to contact your system administrator and ask to have the database's option set to multi-user. The system administrator can do so by using the sp_dboption system stored procedure from the master database, as shown here:
sp_dboption database, 'single user', false