CKEdiitor 4.0 is not compatible with IE 11
you can update the CKEditor Files manually.
in the webassist/ folder, rename the ckeditor folder to ckeditor_bak
On this page:
click the button to launch CK Builder. Select to use the Full Preset, and the Kama Skin.
Copy the downloaded CKEditor folder to the webassist folder in your site.
from the ckeditor_back folder, copy the following three files:
and paste them in the new ckeditor folder.
you will need to clear the browsers cache to see the updates take effect.