(MSSQL) Database is already open and can only have one user at a time

You are getting below error message while trying to perform some activities using the Microsoft SQL Management Studio.

An exception occurred while executing a Transact-SQL statement or batch
(Microsoft.SqlServer.ConnectionInfo)
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Database 'SID' is already open and can only have one user at a time. 
(Microsoft SQL Server, Error: 924)

Solution

Use command, sp_who or sp_who2 to check which user and what is the user currently doing in the database. If the user is idle or no longer usable, please proceed with below activity

Method 1

Right click on database, go to Options. Scroll down to State and change the Restrict Access to MULTI_USER. Press OK to apply to the changes.

Method 2

Alternatively, use below command to set the database into multi user mode.

ALTER DATABASE [DB-SID] SET MULTI_USER WITH ROLLBACK IMMEDIATE;