Unfortunately no luck yet on my end.
It seemed to start happening when the patch was added that made it possible to use Steam instead of Gamespy when hosting. I'm guessing it's at the heart of the issue.
I get a 6-8 second pause when I click 'OK' on the Setup Server screen which I don't remember getting before this issue. I'm thinking it's trying to communicate with something and failing.
Are you sitting behind a firewall at all? I am but I have had no issue with it the past, I tried opening all the ports I could find connected to Arma3 and Steam but it was no help.