The Windows 10 Insider preview build 15025 that released today came with its own share of issues just like any preview build. But surprisingly, this build took it one step further by only being available on PCs running 64-bit.
Dona Sarker noted at the beginning of today's build announcement that the team is aware of this issue. Here is here statement:
We have discovered a bug that impacts our ability to release this build to PCs running 32-bit (x86) versions of Windows 10 Insider Preview builds. Because the majority of Insiders in the Fast ring have PCs running 64-bit (x64) – we decided to go ahead and release this build with 32-bit PCs blocked until our next flight. We plan to release ISOs for this build by the end of the week and Insiders on 32-bit PCs will be able to update from the ISOs.
If you're having issues downloading the build, be sure to check if you're running 32-bit or 64-bit. You can check this by searching for the "System Information" to open the panel. On the right, you'll see the "System Type" which will read x64 or x86 (which is 32-bit.)
Some suspect these updates are being pushed forward due to the impending spring release of the Windows 10 Creators Update. Whatever the reason, PC users with 32-bit machines will be able to download the ISOs straight from the Windows Insider Preview download page once they are available.