I am not getting an 800 or a 4 but when I upgraded my Lightroom to 4 and my Elements to 10, I noticed an issue with ACR.
My Elements is 6.6 as you say, but my Lightroom is now ACR version 7. I have a feeling that 7 probably supports the new Niks.
I did find this: Nikon D800 Images Fail To Open ACR 7 / PS
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Images simply do not open in PS6 / ACR 7 from the Nikon D800
The images were loaded to PC HD using up to date ViewNX2 Correct Answer by Jeff Schewe on Mar 25, 2012 1:30 AM Jeff Schewe
You'll need to download the DNG Converter 6.7 RC which while coming out just before ACR 7 in CS6 actually supports more camers than the ACR 7 version in CS6. The reaso for this is complicated...but the bottom line is that the real time support for various cameras is not a last minute situation. DNG Converter always has the "most recent" camera support. You can find the DNG Converter at labs.adobe.com.