Help with Simple Script to move read 3 day old messages in Apple Mail

I am new to applescript and I am trying to write a simple hard coded applescript to move all read messages that are 3 days or older from one of my inboxes to a different mailbox. My hosted inbox is quite small, so I need to move things out on a regular basis.

Here is my script so far:

set _3_days_ago to (current date) - (3 * days)
tell application "Mail"
	# Inbox for Exchange
	set _msg_list to (every message of "Inbox:Exchange" whose read status is true and date received is before _3_days_ago)
	if (_msg_list's length > 0) then
		move _msg_list to mailbox "Local Inbox"
	end if
end tell

I am getting an error of
error “Can’t get every message of "Inbox:Exchange".” number -1728 from every «class mssg» of “Inbox:Exchange”

I am not sure what to do to address this error.

Looking for ideas, suggestions or other ways to fix/improve this.

Using Mail v4.5 on MacOS X 10.6.7

Thanks in advance,