I have solved my problem. I wasn't saving the incoming files correctly from Dropbox correctly.
I started to use CM Helper and I was still having problems. I would save the game and then it would not be in the Incoming email folder.
When I looked at Dropbox, it appeared that there was a folder for each of the three games we'd started. But in reality, the moves were all in the initial folder I'd created for CMNB.
I made the correction and just opened the first move of the first game I'd been unable to start and easily entered a password and sent the game back to my opponent.
Thanks for the invitations to other games; I will wait until I get my first one completed!!!