Hello Rohit,
Hope you have resolved your issue by now as I understand this a few month's old post.
Nevertheless, if in case anyone else has similar issues, the error 'Cannot set property 'ckEditorUpdate' of undefined' can also occur if the CKEditor's InputId property is not set to the TextArea widget's Id as shown below.

If the CKEditor's 'InputId' property is not set to the TextArea.Id then when screen renders, you will see a plain text area as shown below.

When you start to type into this plain looking Text Area, you get the error as reproduced below:

The plain text area above, is itself an indication that the CKEditor InputId property value is incorrectly set, because when correctly set, then on screen load, you should be able to see TextArea with all the formatting options that CKEditor offers. Typing into the Text Area should no longer produce an error:

Hope this helps someone.