Okay, I keep getting kicked out of the servers with this error message. I googled the problem, and Valve blames it on my connection (though nothing has changed in the past two days, which is when it started)

Here's what I'm running:
PC
Win7 64Bit in Admin mode
Avast! antivirus w/ firewall exceptions
windows firewall is off
Connection is through my school's internet, cable connection. Wireless doesn't replicate the problem, but the game is damn laggy, even on VPN network.

Things I have tried:
running steam in the "friends offline" mode
turning off cloud synchronization
Restarting steam
Deleting clientregistry.blob
Validating TF2 files
Ran the speedtest.net network test (resulting in only this red text: "RWIN is not fully optimized (even though it is a comparatively large number). The unscaled RWIN value is lower than it should be. Also, RWIN being close to and above 65535 does not justify the header overhead of enabling TCP 1323 Options. You might want to use one of the recommended RWIN values below.")


Anyone have any clues? this is super annoying.