I have the same issue. I have a clean list, created at gc.com and try to export some 244 caches, from the vgps to it.
Earlier today I had the "old" problem with no lists showing in the drop down menu. However that resolved itself with a restart.
Then I could choose my pre-existing list and start an export. That freezes, as the TO writes, and nothing more happens until a prompt appears telling me an "unknown error has occured".
Exporting to a .gpx takes forever, it's been more than five hours since I started. Is there any solution or work around?