I am not sure if the for loop you have is doing exactly what it should. I don't know for sure since I can't run it to duplicate what you are doing. I did look on the Perl Monk site and found this. Have you tried it with that module?
I will be honest and say that I am slightly confused by the opening of a new file during the processing or at least that is what it looks like to me. That may effect the loop as well.

           if (-e $NEXT_FILE){
                   sleep 3;        #SLEEP TO ALLOW OS TO SYNC UP
                   close(ACCT);
                   $DETAIL_FILE = $NEXT_FILE;
                   open (ACCT, "$DETAIL_FILE") || die "couldn't open f
+ile: $!\n";
                   $NEXT_FILE = get_next_file_name($DETAIL_FILE);
                   next;
           #NEXT FILE DOESN'T EXISTS, SO SLEEP AND TRY AGAIN
           }
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That is the block that worries/confuses me. I notice on the first file you open prior to the for loop you remove the first line that may be invalid. I don't see any code verifying the other lines coming into the script. That is no test for the correct number of array elements. Could there be bad lines in the data feed that aren't accounted for?