Error: Unable to write code as the combination of code, course number and grade already exists.
Error 400: writeSchoolCode
Solution:
Please check to make sure the code is not expired.
1) From the Board Level, please go to Setup > Codes
2) Then click the ellipsis to show more options and select "Show Inactive codes":
3) Now, search the code you are trying to add and review the effective dates of that code.
4) It is possible that the code you are trying to add has expired?