Vista: The update does not apply to your system

This follows on from the Windows Update problem in Vista and 7 (see here) but seems to be a different problem, so I've moved away from that topic.

I have 32-bit Vista Home Premium (but with a 64-bit processor...don't know why the manufacturer did that), and haven't been able to install any updates since around March 2016. I've followed the instructions on page 1 of the Windows Update thread, and the first update I need to apply is kb3185911. When I try to install, I get the error "The update does not apply to your system". kb3185911 isn't in my list of installed updates, and there don't appear to be any prerequisites for it listed on its page on the MS site. I'm definitely trying to install the x86 (32 bit) version, and not the 64 bit version. Automatic updates are switched off.

To see what would happen, I tried to install some of the subsequent updates referred to on page 1 of the Windows Update thread, but get the same error each time: "The update does not apply to your system".

Any ideas what could be causing this?

Thanks.