Zimbra Desktop 1.0.3 is installed. Logging into Zimbra Mail with IE or Firefox works just fine. When double-clicking an email to view it, replying or creating a new message brings up the, "Oops! Browser is blocking Popups," message. ZD is configured to open a new window when composing a message. We noticed that Yahoo! Toolbar was installed so we removed it, restarted the PC and the message went away. There are no other pop-up blockers installed on the system. ZD was running for about five hours and then the message started to come back again. Closing out of ZD and reopening it fixes the problem temporarily.
Anything else that I can check?