I’ve been struggling with getting FAST search server to work. On a single box installation.
When I installed and configured FAST and created a search site, I did not get any results back.

The only error I got was “The Search request was unable to connect to the Search Service”.

This apparently had to do with certificates. If you open your Certificate store on your local server, you will see a store named SharePoint. In this store (under certificates) there will be a certificate named Sharepoint Security Token Service. I copied this certificate to the “Trusted People\Certificates” store, and voila the error above disappeared.

However I still did not get any results back.

After again some research time, I found that my  Fast Content SSA wasn’t configured correctly. I followed the Technet Guide,  and as it states here you have to open Install_info.txt from your FASTSearch installation directory and use the Content Distributer that is specified there (port 13391). However if you look at the file %FASTSearch Install Dir%\etc\contentdistributor.cfg it will display a different port: 13390.

Reconfiguring my FAST Content SSA with this new port, made my search site return result.