I'm using a child theme for P2, and recently updated the parent theme to v1.5. After that, started getting this error when attempting to add posts or comments on the front end:
Whoops! Looks like you are not connected to the server. P2 could not connect with WordPress.
Did some searches and found this was a problem a few versions ago that was corrected. None of the suggestions for fixing that seem to apply anymore, as the code in header.php is apparently different than it was then.
Thinking maybe there was something with my child theme causing the problem, I switched to the parent theme. Same issue.