SSRS RDL Export Error

Having not worked out the "Column should remain visible while scrolling" nor the Excel format issues, I decided to try another approach. In an attempt to get something like freeze column and/or Excel’s “Columns to repeat at left” and “Columns to repeat at top” working on my report viewer and printed versions of a SQL Server Reporting Services RDL report data table, I broke the table up into four copies each with the same structure and a continuation of the original fields (table 1 fields A-O, table 2 fields P-AD, table 3 fields AE-AS, table 4 fields AT-BG). Each table has the same five groupings (gA, gB, gC, gD, Details). The tables and groups are all individually identified by name, and XML Collections and Elements. The XML export renders fine as does the XML Schema. The report renders fine in the Visual Studio.Net 2005 report viewer and on the web (deployed to report manager). It renders well to PDF, and web archive (.mhtml), but when choosing to export to excel, the following error is thrown.
[Export Error;
An error occurred during local report processing;
An error occurred during rendering of the report; An error occurred during rendering of the report;
Item has already been added. Key in dictionary: 'Group B Value' key being added: 'Group B Value']

What? Why?

If I can just find a direct way to “freeze” the Table Columns within a SSRS Table for the reader and excel export, I’d be good to go!