The kernel changed on an image newer than yours. When there is a difference in kernel versions, you cannot use the plugin server and more importantly, you cannot perform an online update. An online update thorugh kernel changes is problematic. This is why the restriction was added
Your option/solution:
Make an image backup just in case you want to use it again
Create a settings backup
Download the latest image (4.2 023 at time of writing)
Flash the downloaded image
Restore settings