If you are trying to load brushes that are not made for Photoshop 6 then that is why you are getting an error message. For example, if you download a brush that is made for photoshop 7 or CS, then it will not work with photoshop 6.
I know that but what I mean I'm using photoshop 6 brushes. The only ones that work was the ones from photoshopbrushes.com p.s. The other brushes were made in photoshop 6.