Since I didn’t get any responses here I took it to the source and the creator of the XSPF player, Boriel had this to say.
Yes, it’s because you have to include xspf_player.php from within your separated page. The xspf_player.php defines the class name you’r script is complaining about.
In case anyone else wants to add this plug in to your site you can post comments here.
https://www.boriel.com/?page_id=12
Excellent plugin by the way!!!