That 'Bad file descriptor' msg turns up in $! quite often when there is no error, or after error conditions that could have nothing whatever to do with a file descriptor. For example, if you do

>perl -wle "eval{ use Data::Dumper }; print $Data::Dumper::VERSION; pr
+int $!"
2.121_02
Bad file descriptor
[download]

There it is like a bad penny, even though nothing whatever failed in the code.

I'd try printing out $^E and see what light that sheds.

I'd guess that you will get "Permission denied", probably because the IIS6 default user id has changed (*a guess?) from that used by IIS5 and so whatever additional permissions were given to the old userid that allowed it to see the file/directories involved have never been given to the new one. All total speculation, but worth a mention.