Unable to publish reports & Manage Datasources - without Local Admin on Physical Server

I have a SSRS 2008 R2 & W28 R2 server setup. I had setup a folder and provided a user Content Manager previlege for deploying reports from a development server.

But the user is unable to deploy reports. I had to add the user as part of RSExec role on the ReportServer db and then the user was able to publish reports.

But then he was not able to Manage Datasources - so I can given System Administrator previlege. But even then it did not work.

Finally I had to provide Local Admin access on the physical server which host SSRS and then he was able to manage datasources.

Please can someone why this is the case?

Paul - SQL DBA