I just ran into the same problem...and still no answer.
Although I have reason to believe that it is not the SMBIOS.plist as I update any other app without probs (iTunes i.e.) .
I am not able to boot into 64bit either; even after adding arch=x86_64 to the Apple.com.Boot.plst.

So if anybody could please tell us which information is needed in order to troubleshoot.

Cheers