Well PAR (and others) are just "intelligent packers" around your perl scripts. My guess is, that the second package wants to extract the perl58.dll to c:\temp\par_priv.5160.tmp, while the first script has already done so and is still accessing the .dll, hence blocking any write access.

I have no direct solution to this issue, but you might try to set $ENV{TEMP} in the first script, so that the second script is forced to unpack its' stuff to another directory as the first.