Reporting Services permissions on SQL Server

I got this error while i tried to execute report server.
(ser does not have required permissions. Verify that sufficient permissions have been granted and Windows User Account Control (UAC) restrictions have been addressed)

1. Configure the report server for local administration. To access the report server and Report Manager locally, follow these steps:
2. Start Windows Internet Explorer.
3. On the Tools menu, click Internet Options.
4. Click Security.
5. Click Trusted Sites.
6. Click Sites.
7. Under Add this Web site to the zone, type http://<var>ServerName</var>. If you are not using HTTPS for the default site, click to clear the Require server certification (https:) for all sites in this zone check box.
8. Click Add.
9. Repeat step 7f and step 7g to add the http://localhost URL, and then click Close.
10. Note This step enables you to start Internet Explorer and open either the localhost or the network computer name of the server for both the Report Server application and the Report Manager application.
11. Create role assignments that explicitly grant you access together with full permissions. To do this, follow these steps:
12. Start Internet Explorer together with the Run as administrator option. To do this, click Start, click All Programs, right-click Internet Explorer, and then click Run as administrator.
13. Open Report Manager. By default, the Report Manager URL is http://<var>ServerName</var>/reports.
    
    If you use SQL Server Express with Advanced Services SP2, the Report Manager URL is http://<var>ServerName</var>/reports$sqlexpress. If you use a named instance of Reporting Services, the Report Manager URL is http://<var>ServerName</var>/reports$<var>InstanceName</var>
14. In the Home dialog box, click Properties.
15. Click New Role Assignment.
16. Type a Windows user account name by using the following format:
    <var>Domain</var>\<var>User</var>
17. Click to select the Content Manager check box.
18. Click OK.
19. In the Home dialog box, click Site Settings.
20. Click Configure site-wide security.
21. Click New Role Assignment.
22. Type a Windows user account by using the following format:
    <var>Domain</var>\<var>User</var>
23. Click System Administrator.
24. Click OK.
25. Close Report Manager.
26. Use Internet Explorer without the Run as administrator option to reopen Report Manager.

Also, see the following thread (look for post that was marked as answer)