Sharepoint 2010 Claims default login page looping

Hi

We have migrated Sharepoint 2010 classic to Claims based authentication using ADFS 2.0.

It is working for claims ADFS users, but not for CERTAIN (not all) windows domain users.

Issue: When a domain user logs in using the windows credentials (login window) using the default login page (_login/default.aspx?ReturnUrl=%2f_layouts%2fAuthenticate.aspx%3fSource.........) they are redirected back to the login page itself.

I had ran the powershell script for portalsuperuser accounts..

This happens only for certain windows users and randomly. 

What might be causing this issue?

Thanks

Venkat