It seems you are using a non prosilver based style, or the style doesn’t inherit prosilver correctly.
If you are using a style based on prosilver, make sure it inherits prosilver correctly.
If you are using a style not based on prosilver, you will need to create a template for the shoutbox, or ask the style author to provide a working template for the shoutbox.
I don’t provide support for non prosilver styles (Including subsilver2!). This message is only shown to admins.
if you have Paul's Ajax Shoutbox 1.0.2 then the above message appears in place of where the shoutbox would be