Art and Music skill grades are no longer in use for 2017-18 and onward. Please remove those skills from Art and Music classes. This will resolve the skill errors.
The solution is to edit your Art or Music courses on “Schedule > Courses” and change the “Standards” menu to “None”.
You will get a warning, but that is the correct thing to do, to remove the standards (skills) from the Art courses.
For the complete list of 2017-18 skills, please click here.