One of the user is trying to run a report through SSRS report builder from his computer. The same report would work through the SSRS reports website. But when he runs from his computer it fails. On the Report builder - test connections on Data source succeeds.
It errors out with "microsoft.reportingservices.diagnostics.utilities.accessdeniedException". Here is a screenshot. The results Google produced did not help.
http://screencast.com/t/nlxsprwQBefw