I recently moved my entire Joomla server to a new domain. (Same IP address, same ip address for all sites, no other changes made to server)
Unfortunately, the move seems to have kicked off a "fast cgi installer error" on all sites set up with a rockettheme template (I currently have 8 sites using solar sentinal, replicant and terran tribune.) I know there's an issue with the template because the error went away when I reset the site to the default joomla template.
So it turns out that this problem was actually in my IIS settings. When the server was down the timeout errors on the template, overwhelmed the site, so when we brought it back up there was this fastcgi handler issue. I reset the settings in IIS for as high as they would go, and it worked.