Windows 10: ‘An App default was reset’

[German]Some Users of Windows 10 are facing the issue that the file type assignments of apps are reset. The message 'An App default was reset' is displayed repeatedly.


The error description

I first became aware of the problem via this German blog comment. The affected user wrote:

Under Windows 10 1709 we have the phenomenon that the standard apps are reset on various clients. For example PDF on the Edge. jpg, nef etc. on photo.

The problem is that the user may be annoyed by a lot of notifications about this problem in the Info Center.

App default was reset

Furthermore, he cannot open the file type with his preferred application. He wrote that in the event viewer under Shell-core\appDefaults entries of the following type can be found:

AppDefault-Info: SetDefault: Association=.pdf, ProgId=AppXd4nrz8ff68srnhf9t5a8sbjyar1cr723


AppDefault-Info: SetDefault-Info: Association=.pdf, ProgId=AppXd4nrz8ff68srnhf9t5a8sbjyar1cr723, U=S-1-5-21-1078081533-1060284298-682003330-1176, T=2018:05:02:08:21:38, H=uUYaKekA32M=

The user selection for .pdf has been reset to the program ID AppXd4nrz8ff68srnhf9t5a8sbjyar1cr723.

The error also does not occur on all machines. The user concerned writes that out of 190 machines changed over, only 10 systems reported that apps have been reset.

Searching the Internet

I then searched the Internet whether there was a solution. The search for the above entries in the event display has revealed several locations. On, a user complains about this behavior because an assignment of the PDF file format was reset to the Edge after an update.

here is a long thread An App Default Was Reset from 2016 on Technet – a user has problems with Internet Explorer 11 who loses his mappings. Another user complains about lost file type assignments in the image viewer IrfanView. Various apps appear in the thread, from which the file type assignment is removed. Guess: A buggy update or inconsistent apps are the cause.

A fix for the issue

In this [German] article you will find hints on how to assign file types to Apps under Windows 10 using the Control Panel or the Settings app. But this changes with every Windows 10 build.

An explanation of why the problem with resetting the file type mapping for apps occurs can be found in this article. If no user mapping is found or an application writes incorrect values to the User Mapping registry branch, this triggers a file type mapping reset in Windows 10, which then writes back the Windows 10 defaults.

To block, the registry value is NoOpenWith in the registry key:


of the app without a value – as explained in the article. This tells Windows 10 that no selection appears in the Open with popup and prevents Windows 10 from resetting the file to default values. As of Windows 10 Anniversary Update, the value NoStaticDefaultVerb must also be added to the registry key of the app

This web site offers a .reg file which can be used to block the resetting of different file type assignments. This file also sets the relevant registry entries. Maybe it'll help you.

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