[twibbs]

I feel like I am going mad. Well maybe I am, but can anyone help me with this problem:
I'm making epubs from Indesign (cs5.5) and tweaking them in calibre. Everyhing looks OK but when I try to validate them (on Threepress) I'm getting this error:

ERROR: In Search of the Promised Land_ The Politics of Post-War Ireland - Gary Murphy.epub/OEBPS/content.opf(4): attribute "role" not allowed here; expected attribute "file-as", "id", "role" or "xml:lang"
ERROR: In Search of the Promised Land_ The Politics of Post-War Ireland - Gary Murphy.epub/OEBPS/content.opf(4): attribute "file-as" not allowed here; expected attribute "file-as", "id", "role" or "xml:lang"
Here is a section from my content.opf file:

<dc:creator opf:role="aut" opf:file-as="Murphy, Gary">Gary Murphy</dc:creator>

What am I doing wrong? I'm getting the same error from all my epubs out of calibre.
I was doing some post production work in Sigil which did give me valid epubs but Sigil completed ruined all the linked footnotes in the documents (and there are hundreds!) but that's another story!
Would love to hear if anyone has a solution.