Cannot connect to SQL server from workstation - Microsoft SQL Server 2008 R2 (SP2)

Question

I face the following isuse on a Microsoft SQL Server 2008 R2 (SP2):

Login failed for user ''. Reason: An attempt to login using SQL authentication failed. Server is configured for Windows authentication only.

• My SQL server has mixed mode enabled (i verified and switch it on and off several times)
• I am able to loging from a peer server which is a replica with the same windows accounts
• I am unable to loging from a Windows workstation
• The DSN configuration in Windows is succesful though

If mixed mode is enabled why would the server tell me it is not?

What could cause the server to believe it is Win authentication only although the setup is mixed mode?

Answer 1

Wireshark did not help.

I traced back the changes on the server it appears that the main administrator user was renamed. A new sys admin user was created and I had to add this user in both Windows SQL Security groups.