I was on r250, and updated to 262.. tried the default multiplayer example, and it said multiplayer not available.. I downgraded to 261, 259, 255, and 252.. it worked again for 252.
I also tested an exported game from 250, while testing 255, and the 250 worked while the 255 didn't, so it is NOT an issue of servers being down.
There's something wrong with the new versions of C2 (after 252) that prevents connecting to multiplayer server.
I'm guessing it's related to the bug fix in 253 (Multiplayer: false indication of support on Edge)