I don't know if anyone has run across this one. I'm running ZD 1.0 on Mac OS X 10.5.6. I use ZD as my primary mail program, and generally it works fine. However, I have to uninstall and reinstall it at least once or twice a week.
It seems that if I run Software Update (especially one that requires me to restart my computer), the next time I run Zimbra Desktop I get the "Couldn't access Yahoo! Zimbra Desktop server" message. The only way to fix it is to uninstall and reinstall Zimbra Desktop. Then it runs fine again--until I have to restart.
I can't tell if just a simple restart triggers the problem (it's inconsistent), but a software update ALWAYS does it.
Luckily I'm an admin user on my machine, so the reinstall is somewhat less painful; it's more involved for a non-admin user (see my post in the Installations thread).