Excel Services and External Data Ranges

Excel Services cannot render a workbook that contains external data ranges displayed as a table, as mentioned in the documentation.

I had to display a couple of fields contained in a few database tables, in order to use them as a value to be compared against.

The solution: I connected the table as a PivotTable report, with no grouping. It shows the same numbers, but it can be processed by Excel Services on the SharePoint server side.