[German]Some users are facing an upgrade error 0xA0000400 during an attempt, to upgrade a Windows 10 machine to a newer build. I first came over this error 0xA0000400 in Windows 10 Anniversary Update (see the linked German blog post). The installation then stalls. Here is some information about the problem.
Error code 0xA0000400 is reported by the upgrade wizard (see screenshot below) and indicates that something went wrong with the Windows 10 upgrade installation.
(Source: MS Answers)
Unfortunately there is no further explanation – it seems that there is no single root cause. It is noticeable that the error mainly affected users in 2016 in the area of Windows 10 Education Version 1607. In this MS Answers forum thread it becomes clear that something is wrong with the upgrade eligibility.
I also found the error in this Technet forum thread. But there is no solution. The error also occurs in later Windows 10 builds (see below and in this technet forum thread).
Why is the upgrade eligibility missing?
Some versions of Windows do not qualify for an upgrade (see also the upgrade paths here). For example, a Windows Enterprise version cannot be upgraded to Windows 10. Probably nobody will really try to do so.
The error occurs (in my opinion) mainly when an incorrect Windows installation file was loaded, or when using Windows 10 Education version 1607 (see). Regarding Windows 10 Education the error is known and it was known in 2016, that Microsoft is working on a solution. I haven't found a hint, that this has been solved finally.
Try a Disk Cleanup
To ensure that no full system partition or temporary files prevent the upgrade, you should try a disk cleanup as a precaution. Depending on the Windows 10 version, this can be done via the properties of the Windows 10 system drive (right click, context menu command Properties and the Cleanup button on the General tab) or via the Settings page. After the Disk Cleanup, you should reboot and check if there is enough free space on the system drive. The approach is also described here.
A workaround: Upgrade via ISO file
A workaround to install Windows 10 Anniversary Update (or a later Windows 10 build) if the system is eligible for an upgrade would be to create an installation disc with the Media Creation Tool. The Media Creation Tool for Windows 10 may be downloaded at: Media Creation Tool. After creating an Install DVD or an USB install media from that ISO file – or after you have mounted the ISO file in Windows 10 (via context menu in explorer), an update/upgrade can be initiated by running the setup.exe. And if that doesn't work, a Clean Install is required (see also here and here).
The error occurs in Windows 10 V1903
In Mai 2019 users are also confronted with this error when upgrading from Windows 10 version 1903 (May 2029 update). There is a thread about this bug in the Technet forum. There you can find also the hint that no clear cause has been found so far. A disk cleanup is suggested (so that no missing free space prevents the upgrade). Also removing all usb media may help. If this does not help, an upgrade via Windows 10 version 1903 ISO installation file is also suggested.
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