You are not checking the return cordes on any of your IO operations. I find it hard to belive that you are "at a loss" before doing even one round of debugging. any robust Perl code should ALWAYS check the return codes.
It should look like:

mkdir "c:/configs/".$RackID or die "mkdir failed: $!";
open ERROR,">c:configs/$RackID/AP Compare results.txt" or die "open fa
+iled: $!";
...
[download]

pedantics would check returns on the print and the close, but I'd bet dollars to donuts that your problem is in the mkdir or the open. My first guess would be that the program lack permission to write into the configs directory.