Perhaps "back door" is not the right term. I followed the instructions from ACOM/FTM to bypass Mac registration, which can be found here: http://bit.ly/r32k8s
Of the 2 methods offered on the page, I followed the steps for Method 2. Since this fix was offered by Ancestry/FTMM, I did not believe that what I was doing would cause any problems. After first installing FTMM, I had spent weeks, on and off, trying to register it. I also use MacFamilyTree so when I got tired of trying to get FTMM to register, I just set it aside to fuss with later, and continued using Ancestry.com directly, or MacFamilyTree, depending on my needs. The registration problem, which was presented as a temporary issue, never went away. I saw others were having the same problem. Then I found the bypass.
I did not import any FTM files. I merely imported one of my Ancestry.com trees. Everything was working smoothly until today. The last time I did anything was to create a new tree within FTMM on 9/5/2011. Today was the first time I've opened FTMM since then.
I am persistent. I'll keep working at this and will take your suggestions. It's a mystery to me at this point.