Cannot approve a purchase order with a status of "On Hold"

We are using Rel12.1.3 of EBS and are using encumbrance accounting.  We have a purchase order that is a release of a blanket.  We added a line to the purchase prior to raising the Amount Agreed and Amount limit on the BPA.  We have since increased the Amount agreed and the Amount Limit of the BPA, but still cannot approve the PO.  What do we need to do to get the release approved?

Thanks