If you are trying to update to the May 2019 Feature Update for Windows 10 (Windows 10, version 1903), you may experience an update compatbility hold and receive the message, "Mac HAL Driver - machaldriver.sys: Your PC has a driver or service that isn't ready for this version of Windows 10."
Mac devices prior to 2012 or newer Mac devices with the older Apple Boot Camp or Windows Support Software drivers have a compatibilty hold in place and are unable to update to Windows 10, version 1903. Specifically, devices with MacHALDriver.sys dated September 24, 2011 01:57:09 or older in Windows\system32\drivers are affected.
Updating your Apple Boot Camp Windows Support Software drivers may allow you to update to Windows 10, version 1903. You may be able to check for updated Windows support software, in macOS, choose Apple menu > App Store, then install all available updates. You can also try the instructions in the Apple support article here.
We are working on a resolution and estimate a solution will be available in late July.