mysql_fetch_assoc() expects parameter 1 to be resource, boolean given ... in */includes/sessions.php (129)
I got similar error on an OnArcade site and found that the cause was "corrupted" mysql table "on_sessions". I went into phpmyadmin, clicked database name, ticked the *on_sessions table and clicked to Repair.

Result: warning Number of rows changed from 204 to 205

Now page is loading.