Login failed for user Error: 18456 State: 10

Question

In one of my vb.net applications I am getting the error Login failed for user 'user'. But the user has full permission (sysadmin). Also this error happens intermittently.

Error log has the following:

Login failed for user 'user'. Reason: Failed to open the explicitly specified database. [CLIENT: 192.168.1.69]
Error: 18456, Severity: 14, State: 38.
Login failed for user 'user'. Reason: Password validation failed with an infrastructure error. Check for previous errors. [CLIENT: 192.168.1.61]
Error: 18456, Severity: 14, State: 10.
Login failed for user 'user'. Reason: Password validation failed with an infrastructure error. Check for previous errors. [CLIENT: 192.168.1.88]
Error: 18456, Severity: 14, State: 10.

I saw this article.

But in my case all database are set to autoclose OFF.

Also the user exist and has sysadmin permission.

Also KB #925744 is for SQL Server 2005 as mentioned in the article. But I am using SQL Server 2008 R2.

update:

I just saw this article. In that there was query to find ring buffer.In my case i got 0x139F as error code.when i run NET HELPMSG 5023 i got following.

The group or resource is not in the correct state to perform the requested operation.

What does this mean? Whether it will be reason for the error?