I will go ahead and post this 'query' for the benefit of others who might encounter similar problems, even though I have already solved it for myself. This is only the second time in nearly six years that I have had to use the reset button on this PDA. Later: I think I just solved the problem: I did a 'soft reset' on the PDA, and suddenly it resynced with my desktop.

In ZoneAlarm, I have set the Trust Level of both ActiveSync Application and ActiveSync Connection Manager to 'Super.' Ever since I upgraded to Extreme Security, ActiveSync will connect my PDA to my Dell desktop (running under Windows XP Professional SP3), but will not sync the databases. The old: I have a 2003-vintage Dell Axim X5 PDA which syncs with my Outlook databases via Microsoft ActiveSync 3.8.0 (I believe this is the latest version which will work with the X5). Customers using Microsoft Exchange 2003 Service Pack 2 with devices running the Messaging and Security Feature Pack for Windows Mobile 5.0 will benefit from the following feature enhancements included in ActiveSync 4.5: Direct Push Technology, local device wipe, and certificate powered authentication to Microsoft Exchange. The new: I recently upgraded my software firewall to ZoneAlarm Extreme Security (I had been running ZoneAlarm Security Suite for the past four years). I have a mixture of old and new which isn't working.

Microsoft activesync 3.8