A lot of players are currently experiencing this, which pretty much started happening since the latest April 8th patch. You're not out of disk space at all; most likely the developers re-used the same error dialog for faster development, and either left this one behind on error or on purpose.
Most solutions floating around the internet may work for some and may not for others. I've honestly stopped bothering since nothing works for me...
Currently, turning off UPnP on your router settings seems to be having most success. Other solutions include:
- regenerating configuration files (deleting the config files inside the players2 folder)
- regenerating firewall rules (just go into Windows Firewall settings, if enabled, and remove any rule regarding AW, then launch the game).
- launching the game from single player and switching to multiplayer from there.
Many have obviously suggested a Steam repair, without success, since this is a game code issue.
I've also heard of some very bold people that also suggested to disable firewalls and antivirus softwares while turning their DMZ router settings on, but that's like catching a thief trying to break into your home and inviting him in >_>"
So far, I've had CTDs, slow loadings, bugged gameplays, glitched video drivers, even "poltergeists" cranking up my GPU usage for nothing, really (basicly, the game would launch and crash instantly, but the GPU would stay at 100% load until reboot, ACTUALLY HEATING UP). To top everything with a nice, sweet cherry, the mouse works under controller emulation mode, meaning every camera movement looks glitchy as if it was trying to emulate stick movement.
Ah well, IMO, you could try for one of the many solutions that literally fill the community hub on Steam right now, but it'll just be one big lottery. The game will most likely stay broken until the Ascendance DLC comes out by the end of this month. I doubt they'll push two separated updates when they can push only one, not to mention they'll have more time to actually investigate this issue like that.