Adding a custom Purchase Order Printed form to a vendor

HI, 
I created a copy of the PO Form, P0641000 as PS641000. I made a change to the new form to print the discount percent rather than the discount amount at the line level. 
 

This form has been added to the site map and works. 

When I try to add the new report as the default Purchase Order on a vendor, mailing settings tab, I am getting a message that the Report cannot be found in the system.

I think I am missing a step somewhere to allow forms that begin with PS to be used. I have done this with other Acumatcia site, but have changed the name to begin with PO & not PS. 

Is there a way to allow a form beginning with PS to be used??

Thank you