None of the other answers worked for me but I did succeed after a bunch of research.
I installed Windows 10 on new MB Pro (summer 2018) with freshly-wiped hard drive and Mojave installed by restarting in Internet Recovery mode (OS X 10.14 build 18A391).
My first install failed after entering the Windows key, using a build 1607 Windows ISO, with the following error:
Windows could not update the computer's boot configuration. Installation cannot proceed.
Some of what follows is certainly unnecessary.
1. delete the partitions from the failed attempt
Does not delete your files:
restart in recovery mode: restart while holding down cmd+R
in disk utility, click "view" in the top left corner then "Show All Devices"
click on "Apple SSD..." then "Partition"
click on "Boot Camp" then "-" to delete the partition, then "Apply"
quit disk utility then restart from Apple Menu
2. download a current ISO from Microsoft
Using the current (1803) build of Windows 10 may be the only part of all this that is necessary.
https://www.microsoft.com/fr-fr/software-download/windows10ISO
I put the ISO in my home folder, having read that it shouldn't be in Downloads and not wanting it to be in iCloud.
3. disconnect all external devices
Like my USB key with the Windows 10 ISO
4. reset the SMC
Instructions for touch bar MB Pro with T2, other Macs are different.
I used my iPhone for a clock. From shutdown:
press and hold power button for 10 seconds
release button, then wait 5 seconds
press the power button again to turn on Mac
5. reset the NVRAM
Instructions for touch bar MB Pro with T2, other Macs are different
Macs no longer use PRAM. From shutdown:
press power button then immediately press and hold:
option · command · P · R
release the keys after about 20 seconds, during which the Mac might appear to restart (after the Apple logo appears and disappears for the second time)
6. rerun Boot Camp Assistant
It worked like a charm.