Visual predictive check

Dear all, just 2 questions: 1. Could anyone explain what DVIV and DVN mean in visual predective check(VPC)? 2. I try to run VPC with only items: ID TIME DV CMT EVID MDV, and i specified my output file to ".fit" form and in the same path where Perc_V01.pl is (perl version 10). The result was ERROR: NO FIT-files found. I set $my_fit_files_are_in_which_folder=0". thanks in advance. khaled