It's a custom CGI that didn't hang until I put some debugging code in it. I've opened a support case asking for the name(s) of the Windows process(es) I should kill to free up the IPL script. (This was much easier to figure out in Unix.)
It *may* be an instance of iwperl that you need to kill. Any one hanging out long ?
If you download process explorer from sysinternals.com (now part of Microsoft), you can inspect the arguments that were passed to any running process. I have found that useful for killing off errant external and cgi task scripts. Since you had to kill FastCGI, it may be that iw-webd is now running cgitasks in the context of the hosting apache process rather than forking a process. It's been a few years since I've had a misbehaving CGI task.