module/pages/tellafriend/header only supports product_info
because music product links to product_music_info, the tell a friend function does not work with these product.

solution,
add in the filename.php a definition for the product_music_info page
then change this to test if it is a music product

$html_msg['EMAIL_PRODUCT_LINK'] = sprintf(str_replace('\n\n','<br />',EMAIL_TEXT_LINK), '<a href="'.zen_href_link(FILENAME_PRODUCT_INFO, 'products_id=' . $_GET['products_id']).'">'.$product_info->fields['products_name'].'</a>' , '', false);

should be