Jason:
Thank you for your attention. I already solved this issue. For whatever reason, the second parameter in the date-range search, the form field "paymentDue2", was not appearing on the Wizard's list, so it was only searching using the first of the range parameters twice, which was obviosuly anulling most of the searches.
I just added the second parameter manually and it all seems to be working fine now.
Thank you for your attention.