I believe the correction is these two lines:

   apSetFunc(id, AP_Set_Input , 0, 0, '&iFilename' , 0)  &&input file.
   apSetFunc(id, AP_Set_Output, 0, 0, '&oFilename', 0) &&output format and file.

This probably should be:

   apSetFunc(id, AP_Set_Input , 0, 0, iFilename , 0)  &&input file.
   apSetFunc(id, AP_Set_Output, 0, 0, oFilename, 0) &&output format and file.

You were passing a string value instead of the variable value.