The error message in the nohup log is:

Can't use an undefined value as a symbol reference at ./snmpreset01.pl line 50, <INPUT> line #####.>/p>

The input at line ##### is the MAC address gained from searching the logfile for the string, i've grepped out the various lines it says it cannot use and all are valid MACs.

We have this script running in 5 other affiliates and it is not failing there, even though it is doing exactly the same thing.

Have you looked at what line 50 is?

You are not checking whether creating your REPORT file succeeds. Change

open REPORT, ">> ...";
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to

open REPORT, '>>', $report_file
    or die "Couldn't append to REPORT file '$report_file';
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You are not checking whether creating $sock1 succeeds. But you still blindly try to write to it, which might or might not cause your error.

As an aside, you have commented out use strict;. Why?

Sorry, my mistake when I was uploading the script I removed some commented out lines, so line 50 is:

print $sock1 "$mac1";
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So it is trying to, if i read this right, send the MAC to the IP2 on port 5555, but fails because it cannot write to it.