Bitlocker installation fails through Windows Update: 80070643

Hello,

I have been attempting to install Bitlocker on my Windows Vista Ultimate
installation for several months without success.

Every time I attempt to install the program through Windows Update it comes
back with the fail error 80070643.

Investigation of this error seems to relate to problems with Office 2003,
however, I have never had Office 2003 installed on my machine and all the
suggested solutions either do not resolve the problem, or are not relevant to
my setup.

This seems to be quite a common problem but I have been unable to find a
solution that works. Any assistance would be greatly appreciated.