This can happen sometimes if you try to take a DB offline or perform certain other operations and they fail.
Sometimes the lock can be cleared if you close the SSMS instance that attempted the operation, then reopen it. Close and reopen any SSMS instances attached to the server.
It can also occur if you try to take the DB offline while a long query is running. Check the activity monitor and try killing any long-running queries, if applicable and safe.
If neither of the above works, close all SSMS instances, then restart SQL through the SQL Server Configuration Manager. Usually that will cure it, although the DB may be in recovery mode at first.
Check the database is offline or what, check the corresponding MDF and LDF files it may be missing too.
In that case need to restore the DB from Latest Backup.
Sometimes the lock can be cleared if you close the SSMS instance that attempted the operation, then reopen it. Close and reopen any SSMS instances attached to the server.
It can also occur if you try to take the DB offline while a long query is running. Check the activity monitor and try killing any long-running queries, if applicable and safe.
If neither of the above works, close all SSMS instances, then restart SQL through the SQL Server Configuration Manager. Usually that will cure it, although the DB may be in recovery mode at first.
Check the database is offline or what, check the corresponding MDF and LDF files it may be missing too.
In that case need to restore the DB from Latest Backup.
ALTER DATABASE SET OFFLINE WITH ROLLBACK IMMEDIATE
...
ALTER DATABASE SET ONLINE