Aha! Thank you for that explanation, scalesusa...much clearer to me now.

I do update frequently but given this explanation, I will do my part to keep the numbers down :) I am guessing those call numbers must renew daily as it seems to fail early evening but is fine after midnight.

The reason I assumed it was an ebay error is this post:

https://community.ebay.com/t5/Member-To-Member-Support/API-Error-Code-518/qaq-p/24372744