Your new post couldn’t get published after you had activated Private Only plugin. There was conflicts between the plugin code and Prologue code.
Browse prologue theme dir (wp-content > themes > prologue), find and open index.php and locate this :
auth_redirect();
in line 3. Delete
auth_redirect();
from index.php.
Related posts:
Fave Design
[...] Problem with publishing post from prologue theme form? here is the solution [...]