Before build 590 I was always able to click Host and have my own dedicated server. A place where my friend could join me and we could race AI cars. After build 590 came out we had the infamous grey button problem. And now with 660 we are still having the same problem. We both have the same build, both done fresh installed, both have the same vrfmod, and I've made sure that I've forwarded the correct ports (would love if someone could clarify exactly what ports we need to open) We were both able to play on the same ISI server last night but it's not a circuit or car we like hence why we like to make our own. Please, please, please - any help or advice would be appreciated so much. We miss cruising around without fear of knocking better drivers off!
Ok I'm way off from being an expert and this idea is a bit out there, but I experienced the same with being able to connect to my own server when I changed to 660. I couldn't until I changed a setting in the multiplayer.ini and I think it doesn't matter what setting, it just needs to have something changed. I for instance changed the experimental content download speed setting from -1 to 8000 and my join button was no longer greyed out and hasn't been since. That setting doesn't actually do anything, which is why I say it just needs to see a change in multiplayer.ini before it reads the reads the rest of the settings on the first run of a new build. So it doesn't see the http port value. Maybe?? Like I said no expert but it's how I corrected this issue on my own server.
Also try resetting your router as I have since experienced other strange connectivity issues since going 590->600 and resetting my router solved those, nothing else on my network was exhibiting connectivity problems. So my previous "solution" could well have been coincidental in that it seemed to work, whereas a router reset might have also worked. I did say it was an "out there idea" and "maybe" with 2 question marks...... lol
Check the server's multiplayer.ini file. These lines: Simulation Port="54297" // range is 1025 - 65535 HTTP Server Port="64297" // range is 1025 - 65535. Used for file sharing should, I believe, be all you need. (obviously if you change them, you need to forward whatever ports you've set them to!)