Need script that changes subject line on auto-repy message/Entourage

I need to change the subject line on auto-reply messages, but I’m getting something wrong. Everything works fine until the “send autoMsg” line, when I get an error saying that “the message [the old subject line–before the change] can’t be found.” What am I doing wrong? (I’ve tried all kinds of variations and locations for the “set subject” line.) I’m using Tiger and Entourage. Thank you!

set the_subject to "Thank you for subscribing"
tell application "Microsoft Entourage"	
	set theMsg to item 1 of (get current messages)
	set autoMsg to reply to theMsg with opening window and html text without quote entire message
	set signature type of autoMsg to other
	set other signature choice of autoMsg to signature "Newsletter Request"
	tell autoMsg
		set subject to the_subject
	end tell
	send autoMsg
end tell

Now I see the subject is adjusted in the folder where the mail is stored. But in the current view it is not. Anyway to refresh it?