Now I can, Now I can't

I installed the Comodo firewall on my laptop recently to replace the Zone Alarm I previously had.
All was working well for a few days, meaning that after the learning process, I was able to get to the internet (Firefox) and mail (Outlook 2003 and Outlook Express).

However, after a while working on that laptop I found that I could no longer access either of them.
On trying to access Firefox I received the message that Firefox couldn’t connect to the Proxy server.
On trying to access Outlook, I received the ‘Unable to connect to your incoming (POP3) email server’ (error 0x80042108)

I could, though, connect to the internet using Internet Explorer - meaning that loss of the wireless signal was not the reason for the problem.

If I restart the PC, all is well again - implying that the firewall understands that Outlook and Firefox have permission to go through the firewall.
But the problem returns after a while (be it 10 minutes or an hour or two).

I tried re-installing Comodo - but to no avail.
I read that AVG causes a conflict with CF, well I don’t have the Anti-Virus, but I removed the Anti-Spyware anyway.
I ran various anti-spyware/anti-virus checks but found nothing.

Still I have this annoying problem.

Any ideas guys?

Thanks