Hi Nigel,
To have a new namespace you have to add some metadata in it
Here is a sample code
var tn = new Thumbnail(File(FilePath));
var md = tn.metadata;
md.namespace = "http://nb.myCompany.com/mySubject/1.0/"
md.myMeta1 = 3
md.name = "bla bla"
Here you have to new metadata (myMeta1 and name) in the new namespace
http://nb.myCompany.com/mySubject/1.0/
For some obscur raison in some case you have to create a md variable. In other case you can directly access with tn.metadata.namespace and so on
Regards, Michel