iTunes get «class prun» error!

Hello to everybody,
I’ve writen a simple and small script:

if (application "iTunes" is running) then
tell application "iTunes" to get (player state is not stopped)
if result is true then
	tell application "iTunes"
		set playingSong to name of current track
		set LyricSong to lyrics of current track
		set artistSong to artist of current track
	end tell
	display dialog LyricSong
end if
end if

On OSX 10.5 it runs great! However, if I try to launch it on OSX 10.4.11, I get an error:

I don’t understand why it happens?!

Can someone help me?

Thanks in advance!

is running has been introduced in Leopard.
For Tiger you need the old school way

tell application "System Events" to set iTunesIsRunning to "iTunes" is in name of processes
if iTunesIsRunning then
		tell application "iTunes"
			set {name:playingSong, lyrics:LyricSong, artist:artistSong} to current track
		end tell
		display dialog LyricSong
	on error
		display dialog "No track selected"
	end try
end if

Thanks a lot again StefanK!