No, there is no way to uninstall a patch.
Your description makes it sound as if you might have some earlier EPs/SPs which are unpatched. Try patching those first.
Or that you have custom content and/or hacks which are not updated for or otherwise incompatible with AL.
Remote possibility is that when you downloaded the patch it got glorked in the process. You might try installing the patch again and see if that helps (wist that will happen is you'll get a 'Game already patched' message).
If you really don't want the AL patch, the only alternative is an unintsall/resintall.
Just in case, all EA patches here:
http://thesims2.ea.com/update/