BaseCamp not accepting KMZ file in Garmin\CustomMaps Folder

This has been discussed in a couple different threads already. Here's a quote from one of the developers:

The KMZ issues are something that we're hoping to fix in the very near future. What we've since found out is that a number of applications that generate KML/KMZ files aren't writing things according to the standard. Other apps accept these non-standard files and we're in the process of putting in workarounds so we can do the same.

I have the same issue with Custom Maps that I created myself - they work fine of the GPS itself but generate these errors with Basecamp. On another forum, somebody took one of my Custom Map .kmz files, opened it in Google Earth, then saved it back as a .kmz file. BaseCamp was then able to open it. I haven't tried this yet myself, but it sounds like a work-around for the time being.