Hi guys,
its seems like this issue have been faced by many prople. i have checked the solutions on web and found that not all answers contains the complete solution. so decided to put 1 complete solution here.

in most of the places, you will find answers like… Run IE as Administrator -> Open Report Manager site -> Add your user in “System Role Assignment” (settings) etc.

But there is tini-tiny step you have to do before you run your IE as Administrator.

• Open your IE -> Tool -> Internet Options.
• Security tab -> Local intranet -> Sites -> Advanced -> Add your root level site here.
• Advanced tab -> Make sure you have checked (selected) the item “Enable Integrated Windows Authentication*” under Security category.

thats it.

now are you ready to follow … Run IE as Administrator etc.
Here is the what you need to do now: http://www.soheib.com/technical-knowledge/sql-server-2012-reporting-services-uac-user-access-control/

i hope this will help you somewhere.
thanks, khilit