Have you tried looking at this resource? http://onlinehelp.tableau.com/current/server/en-us/help.htm#trusted_auth_trouble_1return.htm
Also, I've moved this post to our Server Admin section where you are more likely to receive a helpful answer.
Typically, I would start by looking at the Windows Event Log on the Tableau Server, and look for the error. You'll find it, and at the very end of the description, it will tell you why the trusted authentication failed. Usually it will be one of the 2:
1. calling IP is not trusted (sometimes, you trust the wrong IP, or not all IP, especially when behind a load balancer)
2. the combination of user / site is not valid (user unknown/unlicensed).
Hope this helps!
Thanks Michel. For some reason it is happened only for one ID and machine combination (same ID in other machine or different ID in same machine there is no issue, so we ruled out that it is not IP issue). As this is development and testing phase, we parked the issue.