@Len-Tidus
That is something that many people do not understand...I only got that error with the default Windows 10 Photo app. Sadly I don't have any experience with 123 Photo Viewer. I can only confirm that the above steps (which are quite advanced I have to admit
that) work for the default Windows 10 Photo App I haven't tried with 123 Photo Viewer nor can I guarantee that the problem will be solved with this app, with the same procedure.
The easiest thing you can try is to open an elevated powershell and use the following command
Get-AppXPackage | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register “$($_.InstallLocation)\AppXManifest.xml”}
Simply right click on the start symbol and open Windows Powershell (Administrator). Afterwards copy the above command and paste it in the powershell (Strg+C and Strg+V) afterwards press enter. Maybe this already solves
your problems. Do you have the exact same error message as the thread starter described?
As the problem already dates back some time I assume an update won't fix it :/. So if this don't work the best suggestion I can give is either contact the app provider directly, maybe they have a better fix, Google
after your problem + the app name or simply use another 3rd party app. That's all I can say for the moment. My long procedure from above probably won't even work because it is intended to be used on the default Windows 10 Photo app so there is a high chance
that this won't even work in your case. Even if you got the commands replayed correctly.