You're not doing anything wrong. You cannot use two of the "simple slider" carousels on the same page. It "simply" won't work. The script 'gets confused' and you get the failure. (There's a longer explanation, but it really doesn't matter) You can use a different slider script if you can find one you like and install it on the same page and it should work, though.
There is this Ning promoted slider (not so simple) that I believe can be used to put more than one slider on a single page-if I remember correctly I used this to put two sliders on my test network just to see if it would work.
Yeah that's right James. Perhaps, you can use different kind of slider in the same page.