Windows 10 - This app can't open

Recently, I've had a spate of requests revolving around Windows 10, and Outlook attachments with Windows Apps. Photos, Edge, etc.

When a user tries to click on a web link, or open an attachment from Outlook when a Windows App is the default application, it throws the following error.

To resolve this, type UAC in  Cortana and click on Change User Account Control Settings
Change this setting to something other than Never Notify

 Once you've made that change, open Local Security Policy and browse to Local Policies > Security Options.

Change User Account Control: Allow UIAccess applications to prompt for elevation without using the secure desktop to Enabled

Restart the computer, and everything should be working fine again.