Update: typo in title, should be Cannot upgrade 64bit Win 8 to 8.1 via AIO (32bit/64bit) ISO. ----------- I've followed instructions for creating a Windows 8.1 AIO ISO (32bit and 64bit versions of all major editions) but when I tried using it to upgrade a 64-bit Windows 8 box to 8.1, the installer complained about it being a 32-bit installer. I know we're supposed to use all the 32-bit base installation files when creating an AIO ISO then "merge" all the install.wim files together to ensure compatibility with both architectures but that only helps fresh installations (performed via boot). Does anyone know of a solution to this problem? I'd like to be able to use a single ISO/disc to both install fresh 32bit/64bit copies of Windows 8.1 but also upgrade 32bit/64bit Windows 8. All suggestions appreciated (except splitting it into two "AIO" ISOs!) Update: As per forum rules, I cannot bump this thread and so I'm going to re-ask (which I guess means create a new thread).