I run Panda Antivirus and I love it.
My computer is:
Radeon 9800 Pro
7200 RPM 160 GB HDD
Sound Blaster Live!
Last night a buddy and I tried a few experiments to get coop working.
If Panda Antivirus is running at all I cannot start the game period. It wont even load.
So I disable Panda from the task tray and voila, I can actually load the game. SO single player works great.
Now here's the wonky part. I try to load coop and I get connection problems. I can almost always get into the lobby, almost always join a game, and almost always actually get the game loading. Every time, the game gets in to a place where I can see my character and it says waiting for other player... a few seconds later... "You have been disconnected"
OK so my buddy and I tried a few experiments.
First I tried unistalling Panda and BOOM! IT works. I could join my buddy's game and we played with out any glitches. We played training and Panama.
Now my buddy also disabled some internet monitoring thing in Norton antivirus at the same time.
Later, I tried reinstalling Panda but setting all six or so panda services to disabled from the administrative tools and rebooting. These services are:
Panda anti-virus service
Panda Function Service
Panda IManager Service
and most importantly
Panda Process Protection Service
Once again I can get into single player but no coop... same disconnect, however my freinds computer crashed on the loading to a buffer underrun... so it may still be possible with merely disabling all the panda services.
Anyways. After having the game since the day after it came out, it was extremely satisfying to finally be able to play coop. Maybe this ill work with other Antivirus programs as well. Id be interested to here what happens with people using different AV programs.
I hope this helps somebody out there.
NOTE. I only sugest unistalling your antivirus if you are confident you are protected and are behind a secure firewall and dont go downloading your email or anything from the net until you have reinstalled your Antivirus software. If you screw up your computer IT IS NOT MY FAULT.