When add a dash in a tag name e.g. "mp3-player" the page where all of the items with that tag "mp3-player" no longer works. Nothing is returned on the page. If I use "mp3 player" or "mp3_player" it works fines but if I use a dash it does not work. How do I fix this problem?

I am using Joomla 1.7.0 and K2 2.5.0. Thank you.