Thanks for trying that simple fix. I've coded all of the registry settings I know of that block it from being loaded into the installer, so it's always worth a shot.
If you click on the PivotTable then press Alt-F11 then Ctrl-G then paste the following into the Immediate window and press enter:
Does it say True?
If not, then you PivotTable is a native PivotTable that's summarizing some table or other data in the spreadsheet or SQL table. You have to have an OLAP PivotTable (that is, one connected to an Analysis Services server) for my add-in to work.
If the above does say True, the next thing I would recommend is to walk through these installation troubleshooting tips:
Keep us posted. I'd love to get to the bottom of the issue you're experiencing.