My friend gave me 5 CC3D boards that he wasn't able to flash. I had this same thing happen on a CC3D that I purchased a while back. It took me forever to figure out how to fix this. If you are having a problem, hopefully it is the same as the one in this video.
If your CC3D won't complete the "Upgrade & Erase" task, this may work for you. The high level steps are as follows:
-Obtain a good firmware
-Flash it to the CC3D through OpenPilotGCS
-Restart OpenPilot & reconnect your board
-OpenPilotGCS should recognize it and be able to upgrade it to the current version.
My CC3Ds have all come from banggood. I only had this problem on the first one I purchased. The others have all been fine. These five CC3Ds were ones my friend gave to me because he couldn't get them to work. He can have them back now. :)
This is the working CC3D firmware used in the video:
Get your own CC3D:
Official resellers include: ReadyMadeRC, HobbyKing or GetFPV
You can get a cheaper one here (full size and mini use the same firmware):
Full size:
Mini (aka Atom):
Nano (I haven't tried this one yet):