The auto-save that is running is searching for a field with name=”post_content”. I believe a quick fix to you’re problem would be to add a hidden field like this:
<input type="hidden" name="post_content" value="" />
This might allow the auto-save to function by simply inserting an empty string for the post_content field of wp_posts table.
I have not had this issue before. But please try this out and tell me if it works for you.