I have just upgraded to Windows 10. I keep getting the message Class not registered when I try to open pictures / photos. I don’t want to lose them by playing about with the computer. Any ideas?

The most likely reason why this error has occurred is because Windows changed the default photo viewer to TWINUI, because it supposedly works better with PNG images. If you cannot change the default photo viewer back to Windows Photo Viewer from the All Apps menu, then try this:

Open File Explorer

Go into the Pictures Folder 

RIght Click a .png image file

Select Open With>

Click on “Choose another app”

Select Windows Photo Viewer

Check the box “Always use this app to open .png files”

Click OK

Now try clicking on other files. If the same error is occurring for other file types repeat the same method by clicking on a file of that type, such as JPEG or for video files. This error may occur with video files as well because TWINUI has replaced other default programs. You will see which default programs it has replaced by accessing Windows System Default Programs (settings icon) from the All Apps menu under the windows icon on the tool bar.