Set Database Back to Multi User from Single User

I am using SharePoint Services 3.0 (SP1) with default configuration options, which installs the Microsoft##SSEE instance of SQL to my local C:\ drive.

While attempting to relocate the files to another drive, I set one of the databases (as recommended) to Single User by using the SQL Server Management Express tool.

I cannot now reset that database to Multi User, even by executing the query

exec sp_dboption 'database_name', 'single user', ''FALSE'

again by using the Management Express Tool.

Can someone please help, in plain english???? Thanks