I have had this problem since the moment I purchased this game from Steam.
I purchased Arma 2: Combine Operations, but the problem occurs for both Arma 2 and Arma 2: AO.
I have tried:
Reinstalling both games
and verifying my game files.
I have a Linksys E3000 Router from Cisco.
Here are my computer Specs:
Windows 7 Home Premium 64-bit
Intel Core i7-2600 CPU @ 3.40GHz (8 CPUs)
NVIDIA GeForce GT 420