Edit listbox from another form

Hi!

I have an app which is a music player. I have two forms: one is the player and the other is playlist  (like winamp) and I have a strange problem.
When I add a value from the player form to the listbox in the playlist form the text doesn't show in the listbox, but the value is there (because when I put MessageBox.Show(playlist.listbox1.Items[0].ToString); it shows me the right text).

Anyone have a solution???

Thanks in advance!