If you're experiencing "Query execution failed for dataset 'ds[Whatever]'. ", more than likely, your warehouse processing is failing. Going into the Admin Console or invoking the web service directly, invoking the Start Rebuild action, I kept receiving a TF221122.
Finally, when I added the account under "Account for accessing data sources" under the "Analysis Services" tab to the SQL Server Tfs_Warehouse database TFSEXECROLE role, processing began to succeed again. Whew.