Thanks for coming to my aid. I am using version 18.104.22.1687 which is the most current. Thinking back to some advice I received from Tech support when this error first occurred in 2011, I tried searching from within FTMM2 for the same census data to link for the same family. I was then presented with all of the family members, save one which was easily corrected to a similar named person in my file. So, the merge is working now.
Perhaps one is only presented with multiple individuals to merge when one does a census search for a family from within FTMM2 and not from the web site back to FTMM2?