I don't know if this has been addressed before, but here is a tip for those of you who use, or have clients who use Mijenix's ZipMagic98 (a cool OS plugin which makes all zip files appear as standard windows folders).

ZipMagic's properties form allows you to create a list of applications which need to view zip files as standard zip files and not as folders. You must include UT Navigator in this list for UTNav to properly download messages. This brings up a related point. If you use a 3rd party lib to view/build zip files directly in your VFP application, you need to inform your end users to include your app in this list if they are using ZipMagic.