I don't know whether this is a development question or a support ticket, so I have hedged my bets and done both
If the support ticket comes up with the answer I will post it here.
I have created a program in my (32-bit) development environment (Windows XP) which uses AF SDK 2012 (2.5).
Unlike with AF Client 2010 (2.4), the 2012 AF client comes in x86 and x64 versions. On a 32-bit OS the installer will only install the x86 AF Client. On a 64-bit OS it will only install the x64 AF Client. (The x86 version is advertised in the installer as "Unsupported operating system"). This is different behaviour from, for example, PI-SDK which can install both flavours side-by-side on a 64-bit OS.
When I try to run my 32-bit program on a 64-bit OS (Windows 2008 R2, where only 64-bit AF SDK exists) surprise surprise, it doesn't work.
If I build my program as "x64" or "Any CPU" instead of "x86", will it then use the 64-bit SDK on the target x64 OS? Will it even build in the 32-bit dev environment where there is no 64-bit SDK? (I'll test this myself but I thought I would get the question out there since there is a bit of time pressure...)
Why is it not permitted to install the x86 AF Client on a 64-bit OS?