Please try “Upload Files” as the option and see if that works. I was able to make that work on the Sandbox 2.0. For some reason the Upload Zip file did not work. There is a known issue when using Safari — that when you download the zip file, it uncompresses the file. In order to work around that, you need to change the preferences to General->uncheck “Open “safe” files after downloading”.
If Uploading Files doesn’t work, please try rebooting your VM.