Blog Comments / EntryModel.owner is undefined
Somewhere in your template you are trying to access the owner attribute on an EntryModel. The example above doesn't show any details on where you might be trying to do that in your templates.

Try commenting out any area of your template where you may be trying to output values that relate to the Entry Model. Maybe even comment out your whole template. Comment things out until you get your page to load again. As you mentioned this error occurs when you try to send a comment, you may also want to comment things out on whatever template gets loaded after you submit the comments.

Once you're getting the page to load without errors, add your code back line by line until you get the error. This will help you isolate where the error is.

When you find it, you'll probably need to add a conditional check to the offending code to get things working:

{% if entry['owner'] is defined %}
    Then it's safe to try to output {{ entry.owner }}
{% endif %}