The instructions on running AUTOLETTER2 include the line: DO AUTOLETTER2,D1
but the appropriate file on the Apple Writer disk is named: WPL.AUTOLETTER2.
Revise the line in the program to read:
DO WPL.AUTOLETTER2,D1 (or the number of the appropriate disk drive)
The Apple Writer ProDOS disk doesn't have an AUTOLETTER2 program. Change the program or rename AUTOLETTER1 as appropriate