Problems with Steam server list and L4D 2 servers.

Hello,

In the last past weeks I had problems connecting to Steam’s server list, and refreshing results in “no internet games responded to the query”.
When I lunch Left 4 Dead 2 through Steam, no group servers appear in the game.
When I set the Firewall Security Level to disabled and log back to Steam I can refresh Steam server list, and the group servers appear in L4D 2. This indicates that there is a problem with Comodo’s firewall settings.
I defined Steam and L4D 2 as trusted application by using “Define a New Trusted Application”. I do this selecting the running processes option and apply.
Unfortunately this doesn’t help.

I wanted to add that this started to occur since a few weeks back, and Steam used to work just fine.

I’m using Windows Vista SP2, Comodo Firewall v. 3.14.130099.587.
Thank you for your help.

Matt