unexpected error occurred while inserting Account records and we couldn't check your work

Hello, I am getting following error in the Customize a Salesforce Object project -> Create Validation Rules exersice.

Step not yet complete in My Trailhead Playground 1

An unexpected error occurred while inserting Account records and we couldn't check your work. Make sure Account records can be inserted in this org, and click "Check Challenge" again. If this continues, contact the Trailhead Help team.