Hey guys,
I figured I should post this here, since it frustrated me for awhile until I figured it out!
When I first got the Neo Myth N64 cart, I installed the newest menu, plugged in the cart, and burned a ROM. No issues!
Then, when I plugged it in again, I kept getting this error (OS is Windows 7 32 bit):

After fiddling with it for awhile, I swapped out the cord. The USB cord was bad.
Thankfully, the Neo team uses a regular mini USB port.

Anyway, hopefully this can help someone else. I don't know if the cords that shipped with other Neo Myths are defective as well.
My order shipped on January 13th, in case the date matters. The cord is sparkly with yellow ends.