It turns out there was a whitespace in my code which I hadn't noticed, so that code works. Thanks for taking the time to reply.

So, that solves one problem. The source data can have many different values for xsi:type, so how to take that into account@?

Yes I did, I change the class Field to the following and compiled? Is this correct?

Class Field Extends (%Persistent, %XML.Adaptor)
{
Parameter XMLNAME = "Field";
Parameter NAMESPACE = "http://www.civica.co.uk/ParisConnect/ConnectXml/1.0/Messaging";
// Property Type As %String(XMLNAME = "xsi:type", XMLPROJECTION = "ATTRIBUTE");
Parameter XMLTYPE = "UDFLookupFieldInstance";
Property Suffix As %String(XMLNAME = "Suffix", XMLPROJECTION = "ATTRIBUTE");
Property Description As %String(XMLNAME = "Description", XMLPROJECTION = "ATTRIBUTE");
Property ID As %String(XMLNAME = "ID", XMLPROJECTION = "ATTRIBUTE");
Property Value As %String(MAXLEN = "", XMLNAME = "Value");
}

The same error is produced.

In my original post I did mention that that xsi:value can be anything, so assuming I made a mistake what would I need to do to this into account?

Hi Alexander

Thanks for the reply, but your suggestion didn't work. 

Andy