i complete all of this but this error occur while check my challenge

Hello @Swetha S,  

You can try the below options

• Clear the browser cache -> Logout & log in again then check the challenge
• Check your challenge in incognito mode/Private Window or a different browser.

If still you face the same error, delete and create it again then try to check your challenge or I will recommend that you create a new playground and complete this task there.