This error is a result of an ongoing service disruption. Please follow status.letsencrypt.org for more information. We should have all of the remaining issues resolved shortly.
In the meantime I'm going to lock this thread since there isn't a need for further discussion on this particular error. Please open a new thread if you need to resume discussion.
Thanks for your patience, we apologize for the disruption and I expect more detailed root cause information will be shared in the near future.