Zonealarm settings need changed

Using WinXP Desktop. I have noticed that when I try to access MG's site, that it is taking ages to load the page, sometimes refusing to load anything. I am even being denied access to other 'favourite sites'.
The only way that I can resolve this is to open up my Zonealarm Firewall (version:7.0.470.000) and adjust the Firewall trusted zone security bar from high down to medium. I have never had problems with this before; always had the bar set at High. The internet trusted zone security bar is set to high also.
Only recent changes to the system i can think of is I changed ISP and installed a new router.
Any help ?