In general, the errors SQL gives are highly useful. Of course every now and again you get one that’s just confounding. The other day I saw the following error in the log:

Login failed for user ”. Reason: An attempt to login using SQL authentication failed. Server is configured for Windows authentication only. [CLIENT: ]

This one confused me for a couple of reasons. First, the user ”. Why an empty user? That’s not really helpful. And second Server is configured for Windows authentication only.

So what the heck is going on? After a bit of searching I found the answer here.

The pertinent quote is this:

Bottom line, the application is trying to connect using Windows authentication, but using a blank/null username and password.

And I was able to reproduce the error just like the OP by using an ODBC connection with no user specified.

It seems that a blank username confused SQL as much as the error confused me.

Aren’t confusing errors fun?