I am having a similar issue: I'm trying to message a user from their user page. As soon as I clink "send" I am taken to a screen that is blank except for the text "Not Authorized To Post". In case it helps, the url for this screen is <a href="https://app.roll20.net/private_message/create" rel="nofollow">https://app.roll20.net/private_message/create</a> I am using Firefox on Linux, but have also tried Chromium, just in case.