Unable to change account picture or lock screen. All users

Hello! First post on this fantastic forum which has sorted me out a number of times. However I can't find a solution for this issue , so I hope someone can help me!

Following a rollback to 8.1 after installing the full release of Windows 10 I've been unable to change the account pictures, lock screens or picture passwords for any user. I've tried the following.

• Create new user
• Registry change and GPE change Unable to change the image on the Lock Screen "'Lock Screen - Microsoft Community
• Deleting account pictures folder
• Taking ownership of, and deleting C:\ProgramData\Microsoft\Windows\SystemData
• Running sfc /scannow, several times after checking component store for corruption

It's driving me a bit nuts now! If anyone has any suggestions I'd be very grateful!

Thanks