Looks like you'll need to reshape your data. The following KB article goes into more detail:
I restructured the data per the KB article referenced. I flattened the data by replacing the FYnnQm columns with two columns, "Quarter" and "Project". That did the trick.
Unfortunately, I did this manually in Excel by duplicating the existing Excel data 7 times (once per FY quarter in the data) and then filling in the Quarter and Project columns. This makes editing the Excel data source more difficult. I need to find a way to script the data input in Tableau to do this automatically, thus maintaining Excel data source editing ease while allowing Tableau use. Any ideas?
I managed to reshape the data using SQL 'UNION ALL', basically automatically duplicating the data for each quarter in the spreadsheet.