Could well be a firewall problem.
Instructions for uninstall of ZA:
In ZA Overview\Preferences, deselect "Load ZA at startup" then reboot pc.
click here and follow instructions for clean uninstall. Either revert ro ZA version 5.5 or use the latest version (6.0.667).
The above link is to the ZA forum. You are more likely to get answers to ZA problems there than by e-mailing ZA.