I fixed this by changing line 111 in the product-rewrite_ebay_links.xml file from
Code:
<validationcode><![CDATA[return (strlen($data) == 9);]]></validationcode>
to
Code:
<validationcode><![CDATA[return (strlen($data) == 10);]]></validationcode>
This took care of the admin CP error, but it wouldn't display the &campid=XXXXXXXXXX bit in the rewritten links. I just hardcoded my campaign ID in the XML file. Ready to keep on rocking.
Thanks for the quick update dismounted.