I had written a nifty new report that I was implementing for a client in CRM 4.0 to be displayed in an Iframe in the Account entity form. After uploading the report using SSRS report manager (http://server_name/reports) and customizing the account form, it worked great for me, but the users got the error "Reporting Services Error...An error has occured during report processing. Query Execution failed for dataset 'DataSource1' "
The first thing to do is turn on the "Enable Remote Errors" feature of SSRS.
1. Open SQL Management Studio and connect to your instance of Reporting Services
2. Right click on the server name in the object explorer and choose properties
3. Click on the Advanced option (on left side) then change EnableRemoteErrors to True
Open your browser and re-run the report to see the actual error you are getting.