I'm getting the same message on the Activity Page itself, Dan. If you just want to acknowledge comments, go to Behind the Scenes and scroll down to Statistics > Comments. I've been able to do it that way. But a word to the wise . . . as soon as you write your reply, copy it. I keep getting logged out due to inactivity??? and if you don't do this, you will have to write it over. If you copy, you can go back in and paste and submit quickly and hopefully it will take.
Strange goin's on today. I'm sure not going to mess with new uploads or anything else that would have me tearing my hair out if I lost it.