Hmm...I just tried (from scratch...I'd uninstalled the plug-in after trying it out a couple weeks ago), and it worked fine for me.
As long as you have Enable Extended Features ticked, it should work (which I forgot to mention, but clever you figured out anyhow). Especially if you successfully transferred epubs before installing the plugin.
I think we'll have to wait for someone who knows more to troubleshoot.
The only advice I can give at this point is try a different cable. Yes, I know it worked before, but apparently if the data section of the cable is slightly damaged, it can be unpredictable about how and when it will work. Many times when people have had that exact error, the cable has actually been the problem, not the programme. So if you have another cable you could try, it just might work!