I also believe its a permissions issue. If you look in the error log for apache, you'll probably find some kind of message stating that it couldn't open /home/foo/slashdot.rdf.

I've tried to reproduce your test, and what happened is that the mirror command silently failed, so that there was nothing left to parse. No error was returned to the browser, so it looks like a parse failure. Always check the error log when perl scripts start misbehaving :)

Solution: you'll have to make the script save the rdf file in some other directory. This directory must be writable by the user that the web server runs as (check for the User option in the httpd.conf file). If you're just playing around, you could use /tmp, but not for anything more serious than that. I always use a dedicated directory.

If the error message is different, post that and it will explain whats going on.