Same problem fo a unit that I just bought three days ago. LIterally. I'm trying to see whether my cords are causing the error, but it would be nice if LIne 6 would address the issue since so many of us are posting about it!
The problem is the port isn't recessed enough for the USB cord to be inserted safely. It's really a shame. I use this at my church because space is so tight. But now I'm seriously thinking about trading it in. And I've had it less than a year. Live and Learn, I guess.