Java Development Tools

I'm trying to use the ViewObject class getRow(key) method, but it keeps returning null. Have scoured the forum and documentation, but cannot find a solution, so am hoping someone can tell me what i am doing wrong.

        ViewObject vo = fixture1.getApplicationModule().findViewObject("MessageDetailsView1");
        Key key = new Key(new Object[]{new Number(90), new Number(1)});
         Row row = vo.getRow(key);

The VO is being successfully updated, the multi-part key values point to a valid record, and yet getRow() returns null. Is there some other step that i am missing, or some nuance. the order of the key values is correct (and for the heck of it i tried the reverse order - new Key(new Object[]{new Number(1), new Number(90)} - to no avail)

am using JDeveloper 11g.

Thanks for your help!