I have three different hosts at DYNDNS that recently stopped updating via my ERLs. I couldn't trace back exactly when they stopped. It might have been with the 1.9.1 alphas or before. Anyway, I think that 1.9.1 is unrelated.
I had been providing my normal DYNDNS username and password via the Edgemax GUI which DYNDNS accepted happily. Apparently now they are enforcing the use of your Updater Client Key (found here https://account.dyn.com/profile/) instead of your normal login password. It probably relates to the recent DDNS attack they suffered.
Anyway, I stumbled around for a while trying to figure out if 1.9.1 broke something or I did. The logs showed a bad authentication so I changed passwords, retyped etc but it kept showing the same error. Eventually, I found this post https://community.ubnt.com/t5/EdgeMAX/Can-t-get-dyndns-to-update/m-p/1422751#M89346 in this forum and it fixed my problem. I thought I would drop this post out there in case anyone else was having the same problem
