While adding contract to exist Purchase order it throws error 'deselect the price or uncheck invoice expected

Hi All,

i tried adding contract to existing Purchase order in order status, it  displays the error  as 'Deselect the price or uncheck the invoice expected indicator'

This is a material PO created on 10th September 2015  and contract validity  date for this material XXXX in condition tab is  from10th October 2015.

Please explain  me is this a standard correct flow of PO .

Thanks & Regards,

Srini