Why did SQL Server go into single user mode?

Question

I've had an application that's been running great for several months. Thankfully I use try/catch blocks in my database calls because this morning I get an email alert from my catch block that said,

Message: Login failed for user 'NT AUTHORITY\NETWORK SERVICE'. Reason: Server is in single user mode. Only one administrator can connect at this time.

Source: .Net SqlClient Data Provider

Data: System.Collections.ListDictionaryInternal

So I go and try to access the application, and yep, verified that it doesn't work.

I was able to remote desktop over to the server and log into SQL Server which suddenly "fixed" the issue, but I don't know why this happened. ("Fixed" as in now the application does it's normal CRUD operations.)

Does anyone know why this might have spontaneously happened?

Also, if I go to database -> properties -> options -> State, I verified that Restrict Access is in "MULTI_USER".

The app is powered by the mighty SQL Server 2005 express. Is that the problem?

Answer 1

Did you check your Windows Event Logs to see if anything happened to the server? Did it reboot after installing any updates?