Purchase Order Reapproval Issue

I have a order that has previously been approved and when a user makes a change to this order such as Quantity it should go back for approval.  However I receive a red error and the system blanks out the line type

As you can see the line type has been blanked out.

Now the processing options on the Approvals tab of this version are seen below:

Also you can see the order activity rules for this order type (OP) and the line type before making the change is S.  Currently the order is at status 230-280 and then the user wants to make a change and for it to go back for approval.