SO Release can't mark Ready to Fulfill

I have an open order and on Line 2 Rel 1 I can’t check ready to fulfill, it is grayed out. Is it because I have one item has been shipped against the Release?
Order Rel was for 11 and we shipped one

Do you have AMM (Advanced Material Management)
This check box can be used to allow allocation of product in the fulfillment workbench when the order is ready to be fulfilled. Checking the box may be based on some business rules of the customer passing a credit check, etc.

I figured it out. It was closed the new changes with it saying closed but not checked made me think it was open. But I opened the line and they could open the release.