Importing idoc into single stack PO (7.31)

Hi,

I have a custom idoc and I want to import the meta data into our system. When I attempt to import it I receive an error

But when I attempt to import it into our dual stack 7.11 system from the same ECC system via IDX2 it works.

I am told that the iDoc is not released and that may be the problem BUT as I can import it into PI but not PO I am assuming that PO is a little more fussy about this. Can anyone suggest a solution, except for releasing the iDoc?