This Post by Adam Saxton saved me hours of time today.
I setup SP2010 with SQL 2012, all appeared to be working until I create a rdl and tried to deploy it into SharePoint from BIDS in VS2010. Got the error: The permissions granted to user are insufficient for performing this operation. reporting services + AccessDeniedException.
Resolution: This is a permissions issue on the SharePoint site, I opened the url http://<sitecollection>/_layouts/people.aspx?membershipGroupId=0
I had 2 identical accounts: demo\administrator & DEMO\Administrator. I ran the select statement explained by Adam to check the user table on the content db where the site collection sites:
SELECT tp_login, tp_title, tp_delete from UserInfo
I deleted the NT account (not the claim account) using the SP UI (http://<sitecollection>/_layouts/people.aspx?membershipGroupId=0). Re-ran the T-SQL query and the offending NT account (DEMO\Administrator) has been virtually deleted by SP.
I can now publish the report.
More Info on setting up SSRS for SharePoint: