NL (Last) Still Won't Work

I am trying to get Jet to pull the last date that we paid a vendor (or the last document date related to that vendor invoice). Basically I want the report to weed out vendors that we haven't used for years. I found this post related to NL(Last): http://community.jetreports.com/viewtopic.php?f=7&t=3074&p=9223&hilit=nl+last+#p9223 , plus this one: http://kb.jetreports.com/article/AA-00779/0/ .

It seems that no matter what I do, NL (Last) pulls the first record. Here are a few of the functions I tried:

=NL("Last","Vendor Ledger Entry","Document Date","+Entry No.","*","Vendor No.",$D8)

=NL("Last","Vendor Ledger Entry","Posting Date","+Posting Date","*","Vendor No.",$D8)

=NL("First","Vendor Ledger Entry","Posting Date","-Entry No.","*","Vendor No.",$D8)

Am I doing something wrong? Thanks in advance.