It appears there is a limit on the number of children perl can have under windows:

http://code.activestate.com/lists/perl-win32-users/12064

However that thread says the limit only applies to concurrent threads that perl can wait on. Perhaps your code is creating child processes to convert each PDF, and then not waiting on each process, but is leaving zombies.

In reply to Re: Win32 limit to number of calls to system()? by chrestomanci
in thread Win32 limit to number of calls to system()? by Limbic~Region

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