Win10 Cortana failing with "Activation of app [...] CortanaUI failed with error: The remote procedure call failed"
Solution 1:
I had this problem also. To fix it I had to go to the folder:
C:\Users\%USERNAME%\AppData\Local\Temporary Internet Files\
right click, properties, security tab, add the group "all application packages" and give that group full control. once i did that i could get into all of my metro apps again.