Hi Community,
It appears these error messages were occurring due to a hiccup with a little site update we pushed out to fix an issue that was causing the "Custom Item Specifics" link not to show up for some categories. We are not seeing these errors any longer so you should now be able to create and post listings again without receiving these errors.
Please let us know by contacting our customer support team or posting to this thread if you continue to receive errors of this nature.
-Mike