the problem may be related to Microsoft's SR2 for Windows. After I installed it I had problems with connecting as well. (I also use Dynoplex software)
I corrected the problem but uinstalling the handeld and the Blackberry Desktop software from my Windows machine and reinstalling the latest versions. The problem may arise again if you install any software that installs via an *.exe file (like eOffice) rather than directly through the Application loader via an *.alx file. (Don't ask me why - it's beyond me!)
Just repeat the install uinstall process again.

Or hang on till os4 is released and ditch bill gates for good! :P