Hi Jyothi,
From the traces, I think you should look into the standard content permission,
Navigate to the Portal Content Directory (PCD) via Content Administration -> Portal Content
Within the PCD navigate to Portal Content -> Content Provided by SAP -> End User Content -> Standard Portal Users -> iViews -> com.sap.km.iViews ->
Here, in some folder, you will find the KM Navigation iView Templates which is usually used / called during content rendering.
I think, some permission is missing here.
Try and give the access of Read and Enduser to the user directly and see, if that could solve your problem.
Give it a try....
Thanks,
Biroj