Try installing an older Disco mod, like 4.84 and see if you can use the 1 player. If so, it's the openSP thats not letting you play SP in .85.
Some other things i noted reading your posts:
Make sure you are doing a complete install of FL, and NOT express install. (helping one person for 6 hours, this turned out to be the problem. I could have killed him.)
Do NOT disable your anti-virus, do a complete uninstall before installing FL.
Have the FLMM running while installing the disco mod.
Delete all other mods(recommended, not necessary), at the very least for the troubleshooting stage to eliminate any conflicts that may have been created with the older mods since Disco is a new mod now.
So far, helping about a half a dozen people to connect, it seems like most cases of not being able to connect are unique to each person and their computer. So be patient and keep trying. Remember to follow each instruction you try fanatically.
