Can't import excel file with multiple worksheets

I'm trying to import an excel file into a TMS grid using FlexCel and TMS Grid Filters ( 

When I installed AdvGridFilters, it came with a demo called SimpleImport. If I load up this demo and choose any excel file that has multiple worksheets, it loads the worksheet names on every tab and resizes the table cells correctly to display the data that should be there, but the data is completely empty on every worksheet tab. If there is only one worksheet, the data loads fine in the grid. I've tried creating a brand new excel spreadsheet in Excel 2010 and giving it two very simple worksheets and the demo still won't load the data when I try to import it.

How do I load the data from an Excel file with multiple worksheets? How can I adjust the demo to do this? 


I am not sure on what can be going on: I tried the demo here with many files with multiple sheets and in all cases all sheets where imported.

Can you send me an example file to that I can test?