I got an error: "1'' is not a valid program or does not exist while creating an email alias

I got the following message while creating an email alias using the "feed to program" on advanced tab:

Edit Mail Aliases ->Mail Aliases->Add an alias to this domain
select "Advanced mode" tab
Name: checked "mailbox" and input the alias name
Alias destinations: selected "Feed to program" and input the program path
Clicked "Create" button
Got an error: Failed to save alias : '1' is not a valid program or does not exist

I don't know what is '1'.
And, all the destination files do exist.

Please tell me how to fix or workaround.

Thank you.