I faced this error few times on different scenarios. For ex: one user cannot connect to SQL server using SSMS or Application cannot connect to SQL server. This usually happened to me when there was a change in the system like user computer has been replaced or there were some network updates.
- Some times just by rebooting the user machine I was able to resolve the issue .
- For today , I had to move a DB from Dev server to QA and when application configuration file has been modified to use the new server info I could not connect to it. When I checked the SQL logs surely I saw ‘. Login failed for user ‘xxxx’. Reason: Login-based server access validation failed with an infrastructure error. Check for previous error. When I launch the SSMS on the SQL server itself I could connect to it using the same user, which means there is no problem with the authentication. But when doing the same across the network it has issues meaning it needed specific permissions on TCP endpoint . I used the below query to do this and it resolved the issue
"TSQL Default TCP"
Below site has detailed explanation of all the infrastructure errors with severity and state