SSRS portal failing to run multi-table report

I've searched and read everything I can find, but am still battling two reporting issues. Both dealing with Excel. My guess is they are related.

Our SSRS Portal shows its version as "Microsoft SQL Server Reporting Services Version 11.0.2218.0" and the reports were created in VS 2010 Ultimate, with "TargetServerVersion" set to "SQL Server 2008 R2 or later".

My suspicion is that there is a hidden setting on the SSRS portal, similar to the visual studio "TargetServerVersion", that needs to be set for Excel to work correctly.

My critical issue is that I can run a report, with seven tables, via VS 2010 and export it to Excel to get an xlsx file with seven tabs that are correctly labeled for their content, but every attempt to run the report on the portal is failing. I don't even get to the point of exporting. It is failing when it tries to run the second dataset.

My second and minor issue is that I have random, single table, reports failing their distribution if I set the output to Excel. CSV works fine.

Thanks in advance for your help.