Sounds like you didn't unpack the patch correctly, or that you are using something other than a 1.04a install base. If you're certain that you started from a 1.04a, then you could try unpacking the patch again.
To be sure, though, you should probably uninstall, and delete all files. Then do a fresh install from CD, add the 1.04a official release and then download the 10/17 beta. When you unpack the beta, make sure you're unpacking it into the root CK folder.
There are one or two nobles in the 1066 patch that will CTD (a scenario file error for which I will fix with the next beta), but the rest should pose no problems. I've loaded successfully as England, France, Aragon, Castilla, Denmark, Byz, Gernany and others many times since Sunday and the vast majority of the others are fine too.