Property of non-object notice after submitting CiviCRM Webform with Contributions
A couple of quick thoughts:

upgrade to Webform CiviCRM 5.x (we’re no longer supporting 4.x)

Edit: we have now officially disabled support for D7 - 4.x - you will now have a ‘unsupported version’ warning in your Drupal status report.

what is your PHP version?

always switch off notices on production sites: goto admin/config/developement/logging and set to -&gt; None

open an issue on our drupal.org webform_civicrm project page and give us exact steps to reproduce