I got that too, although the plugin seems to be functioning.
It’s line 84 in wpgform-post-type.php that’s causing it.
if ($content !== get_the_content())
wp_update_post(array('ID' => get_the_ID(), $content)) ;
Changin it to
if ($content !== get_the_content())
wp_update_post(array('ID' => get_the_ID(), 'post_content' => $content));
Seems to fix the issue (although I haven’t read most of the code so I’m not 100% sure what’s going on there :)).
