http://www.scorehero.com/forum/viewtopic.php?t=41538
People having the same problem:
"I'm having the exact same problem. With both my guitars. The X-plorer and the Les Paul.
the x-plorer started doing this mid-song while a friend was playing. The les paul was after I changed the batteries because the guitar was lagging (strums and fret pushes were registering close to a second late, and batteries looked low). This was not the first battery change. More like the 4th/5th.
As soon as I turned it on with the new batteries it started downstrumming forever. I can stop it by detaching and re-attaching the neck, but as soon as I strum down again it starts.
I took the X-plorer apart to find out what was wrong, and it seems that the down-strum button is always making a connection, or not at all. Regardless of how many times you actually phyiscally press the button. So I would assume the button is fucked, and should be replaced with a new one. But I'm too busy to go buy a new button and solder it on to replace the old one in my X-plorer, and I'm hoping to make good on the warranty for the Les Paul, so no news on whether this actually is a viable fix.
If you find anything else out let me know. Until then, I'm a controller hero I suppose."
It seems pretty difficult to fix, but browse that topic and see if you find anything.