I swapped out the cable modem - a Netgear CM400 with an old Comcast modem/router that I had replaced because of its poor signal strength. After a few minutes, the Microcell activated successfully with no further intervention from me. So the only conclusion I can come to is that the CM400 was indeed the culprit. That's disappointing, given that I bought it to replace what I felt was an inferior device provided by the cable company.
I don't know if you've had other reports of the CM400 not working with the Microcell, but it might be worth noting so that you can identify similar problems quickly in the future. Anyone want to buy a slightly used Netgear cable modem? 🙂
