XML Validation: "No Child Element Is Expected At This Point"
Your itemList is currently made of exactly one item; that is because the default particle cardinality is 1 (minOccurs = maxOccurs = 1).
If you wish more than one, then you need to add maxOccurs attribute with the appropriate number; for unlimited, use maxOccurs="unbounded"... like so:
<element name="item" type="co:itemType" maxOccurs="unbounded"/>
In my case I got this message because the ordering of the fields in my XML did not match those in my XSD, I had erroneously reversed the order of the last two fields.
While this is not the situation in the question, I thought it may help others who are drawn to this question by the title (doubtless I will reference this question again in the future when I have forgotten what I have just learned).