annoying trial version alert won't go away!!

hi

for some time now i have had an annoying alert that pops up after i play 5 tracks in itunes. i am presuming that it is for some itunes plugin/software, but i have uninstalled all such software that i am aware of and still it comes up. the alert says:

"TRIAL VERSION

Purchase the licensed version today! This trial version will only work for the five songs you play each session."

and then there is an OK button which clears the alert.

does anyone have any idea what might be generating this alert?

thanks

nick