A couple of things

It would be useful if you could isolate/tell us where the "Access is denied" msg is being displayed? Also, if you could isolate which line of your script is causing it.

Maybe the easiest way to do this would be to use Perl's built-in debugger.

Second point, and I hesitate to mention it as you say that "this is working 80% of the time", but...according to the Win32::EventLog docs:

$handle->Backup(FILENAME);
The Backup() method backs up the EventLog represented by $handle. It t
+akes a single arguemt, FILENAME. When $handle represents an EventLog 
+on a remote machine, <b>FILENAME is filename on the remote machine an
+d cannot be a UNC path</b> (i.e you must use C:\TEMP\App.EVT). The me
+thod will fail if the log file already exists.
[download]

Which if interpret correctly means that the built-in Backup() method will only work if the source and destination are on the same machine? And reading your code, it appears that you are suppling a local path ($locdir) whilst processing a remote machines logs?

It strikes me that the size related problem could be due to memory exhaustion?

Kick me if I mis-read this.