Board Thread:Support Requests - Getting Technical/@comment-29715441-20160821181407/@comment-8-20160824172224

It's called a session error, an is the result of the system thinking you have been gone so long you must have logged out (or something like that).

Anyway, what it shouldn't do is lose your work in the process of showing the error. That's a bug, and it's been listed for the techs to look at

In the mean time, I suggest copying your text before clicking "reply" if you have had the page open for a while. And, as ThePhoenixGirl says, refreshing should make it go away.