During my tenure there, there wasn't any way (that I can remember) to prevent someone from posting privately when they can post publicly. But maybe it has to do with account type? I really don't remember any accounts being unable to post privately, though. Edit: I'm getting the same error. Is anyone else? Maybe it's a system-wide glitch over there? Edit 2: I get the same error when trying to post a public message. What's up with that? Edit 3: Others are posting, but not very much. Makes me wonder.