One of my customers is still using Windows Live Mail as their default email client. They're currently running the Windows 10 1709 "Fall Creators Update," and sometimes for whatever reason they lose their ability to scan to email from their Brother MFC-7240 through ControlCenter4.
In previous versions of Windows 10 you could open the old control panel and go to Set Program Access and Defaults (SPAD), click on the custom radiobutton and choose live mail to fix this issue. Since the release of 1709 the link to SPAD opens up the settings app and takes you to the Default Apps page. Unfortunately choosing Windows Live Mail as the default handler for mail here doesn't fix the problem.
It turns out that this is because ControlCenter4 is using the default MAPI settings, not the default program setting that this app lets you configure. As the MAPI registry key is no longer updated when you set a default program, CC4 can't see the setting and throws this error.
Changing the default MAPI client using the registry.
Run regedit and open this key: HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail
You will notice that there are different sub keys for each folder. One for "Microsoft Outlook", "Outlook Express", "Opera", etc. these are the registered mail clients.
Inside the Mail folder there should be a value called "(Default)". You need to change the value to the name of one of these subfolders
For example, since I want to use Windows Live Mail, I open the "mail" folder, double click on the "Default" key, and set its value to Windows Live Mail
After hitting ok it works. If you want to use a different client just set the key to the name of one of the other subfolders in the mail folder and it should work.