Messenger goes from Away to Online automatically

I have Messenger version 6.2. After installing Sygate Personal Firewall, when I leave my Messenger on for extended periods, my status will change from Away to Online by itself. If I leave for a few hours and come back, sometimes it will do that, and sometimes it won’t. Sometimes I can leave it for a few days, and my status won’t change. It’s very sporadic. I uninstalled Sygate and tried Norton Personal Firewall, but it appears I am having the same problem. Has anyone expereinced this? If so, how did you resolve it? I would like to keep a firewall going on my computer. Thanks in advance.