I am trying to use Drill Down Builder or any standard Drill Back to the Receivings Transaction Inquiry Zoom window to be used in SSRS. In Drill Down Builder, I created to drill back to the Form with only the parameter POP Receipt Number. I've tried using multiple combinations with POP Type, (L) Type, and VendorID with no luck. It seems to interact with the window but gives the following error: "The POP Receipt Number field can not be set because it has been locked." Then does not open the window.
This is the way Drill Down Builder is setup:

Expression Action in SSRS: ="dgpp://DGPB/?Db=GP2913&Srv=ROSESQL29&Cmp=SWISS&Prod=3830&Act=OPEN&Func=RCVG&POPRECEIPTNUMBER="+TRIM(Fields!POPRCTNM.Value)+""
Any help getting this to work would be much appreciated!