After looking at dozens of different user reports, it’s clear that this error has a couple of different causes that might be responsible for this error while attempting to use the Windows Upgrade Assistant utility to install Windows 11. Here’s a shortlist of potential scenarios that might cause this issue: Now that you are familiar with every potential scenario that might be responsible for this error, let’s get to the part where we help you fix the issue. Below you’ll find four different methods that other users finding themselves in a similar situation have successfully used to get to the bottom of this issue.
Uninstall Virtual Box / VMWare (if applicable)
As it turns out, one of the most commonly encountered causes that will cause the 0xa0000400 error when using the Windows Upgrade Assistant is a conflict between Hyper-V and the proprietary virtualization technologies present with Virtual Box and VMware. In case you’re trying to upgrade to Windows 11 and you have Virtual Box or VMWare installed on your older Windows versions, the first thing you should do is installed the conflicting software to make sure the upgrading process is successful. Note: After the upgrade to Windows 11 process is complete, you can easily re-install the virtualization software that you’re using. If this scenario is applicable, follow the instructions below for instructions to get rid of the 3rd party virtualization software that is conflicting with the Windows Upgrade Assistant: In case this method is not applicable in your case or you’ve already tried to uninstall the conflicting software but the same error is still popping up, move down to the next potential fix below.
Perform the Upgrade from mounted Windows 11 ISO
If the first method was not applicable, the next thing you should try is to complete the upgrade to Windows 11 by downloading and mounting a compatible Windows 11 ISO. As of now, WUA (Windows Upgrade Assistant) is still a very buggy utility and should be avoided. You’ll better off just mounting an official Windows 11 ISO and performing the upgrade directly by opening setup.exe on the root location of the ISO. This method is confirmed to work by a lot of users that we’re previously encountering the 0xa0000400 error while attempting to use the Windows Upgrade Assistant. Here is the exact process that they followed in order to bypass the 0xa0000400 error when upgrading to Windows 11: If this method didn’t work in your case, or you’re looking for a different method move down to the next potential fix below.
Use the Media Creation tool to Upgrade
If the method above (mounting a Windows 11 ISO file directly) did not work in your case, you can always use the MCT (Media Creation Tool) to burn a DVD or turn any flash drive (over 8 GB) into a compatible Windows 11 installation media. After you do this, you can change the boot order accordingly and perform the upgrading procedure directly from your flash drive. Prerequisites: On top of an Internet connection, you need a blank DVD disk of at least 8GB and a DVD Burner or a flash drive of at least 8 GB of available storage. If you meet one of these requirements and you are prepared to go this route, follow the instructions below to use the Media Creation tool to upgrade to Windows 11 and avoid the 0xa0000400 error: If this method is not applicable in your case, move down to the next potential fix below.
Change license key to PRO version (Only for Workstations)
If you’re encountering this issue while attempting to upgrade a workstation to Windows 11, you should ensure that you’re using a PRO license key before attempting to initiate the upgrade. Just to be clear, you don’t need to buy a new PRO license just for the sake of being able to upgrade – you can simply make the switch to a generic Windows PRO license key prior to initiating the upgrade. If the upgrade is successful, you can then revert back to your regular license key. Follow the instructions below to change the license key to PRO: Note: If the upgrade to Windows 11 is successful, you can return to your previous license key using the same procedure shown above (steps are almost identical on Windows 11)
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