How to resolve the error about 'A partially-completed form was found'? Yesterday I have updated Webform module from 7.x-4.0-beta3 to 7.x-4.13.

After doing so, I am getting this notification message, throughout the site:


  A partially-completed form was found. Please complete the remaining portions


I have also checked some threads.

When I check log entries I got this error :


  Notice: Undefined property: stdClass::$is_draft in webform_client_form()


And deleting partially filled nid in webform submissions table is not working for me.

What can I do with it?
Since "deleting partially filled nid in webform submissions table" (as in your question) seems to not solve your issue, you may want to have a look at comment nr 2 in issue 2560907, which states:


  A webform node is being displayed on that page and there is a draft submission for the current user. You don't have to find the id -- the form will be displayed, unless theming or another module is preventing it.