I solved this by loooking at the log property of the dxl object.
It said non existent file was the problem which was silly as I had the notesdocument and it's size was big enough to include the attachment.
Now I had another problem earlier which I solved by deleting the uidoc context and this solved this problem as well.
I moved the code up earlier in the code.
Basically the dxl was referencing an already loaded version of the document via the uidoc.
by adding this code in, the problem was solved:
Dim uiw As New notesuiworkspace
Dim uidoc As notesuidocument
Set uidoc=uiw.CurrentDocument
Delete uidoc