Are the x64 clients not updating since they were installed? None of them is receiving updates?
Sometimes, with all correct configuration in place, they don't update; what I usually do is kill the rtvscan.exe process and delete the usage.dat, and sometimes even the virusdefs.dat, in the programdata\symantec\definitions (vista) or program files (x86)\Common files\symantec shared\Virus defs.
Then I force a policy update and many times this fixes it - all this with a batch file.