Problem:

I get the following error when I attempt to view reports:

An error has occurred during report processing. (rsProcessingAborted)
Cannot impersonate user for data source 'TfsReportDS'. (rsErrorImpersonatingUser)
Log on failed. Ensure the user name and password are correct. (rsLogonFailed)
For more information about this error navigate to the report server on the local server machine, or enable remote errors 

Solution:

Verify that the password for the account reporting services is using has not expired.

Explanation:

In your browser, navigate to http://localhost/reports (from your reporting server machine).
Click on Tfs2010ReportDS on the home page. Under the 'Credentials stored securely in the report server' click the Test Connection button. You should see the following message "Log on failed. Ensure the user name and password are correct."
Simply reenter the username and password information and test the connection again.