The first suggestion, to leave off the HTTP response header, didn't change my result.

The second suggestion provides meaningful feedback though. I built the Hello World script as you suggested, and it would not execute with the name "test.pl" - I got the same error as before. However, when I changed the extension to cgi, I got a web page with the content "Hello, world!", which is very exciting. I changed the extention of dcdot.pl to dcdot.cgi, but I get the same error. I cleared the cache and tried again, in case, but still not joy. Still, this confirms that I have IIS configured to interpret Perl scripts, which is a good first step.