That warning has been gone for a while. Please ensure all your machines are up to date. I'm pretty sure that was fixed about 6 months ago in the 12 release cycle.
The cause of the problem is that you're trying to back up an insanely huge number of files. You need to reduce the number of files you're backing up. You could put something like this:print "$d\n";
after that foreach and you'll see the directories it's trying to back up, which will help you remove the erroneous entry.