It looks like you need to setup a dummy entry in the User Section of the page shape sheet to accept the formula.
Let's say for sake of argument, it is User.Row_9. In the User.Row_9 Value cell, enter this formula:
SETF(GetRef(User.ID),"=setf(getref(Sheet.1!User.set" & Sheet.1!Prop.ID & "),Sheet.1!Prop.Val)"). This ends up pushing this formula into the User.ID cell => SETF(GetRef(Sheet.1!User.set5),Sheet.1!Prop.Val)
In my test case, Sheet.1!Prop.ID had value = 5, and my Sheet.1 has a User.set5 row. Now edit the User.Row_9 formula to reflect your exact needs.