There are 4 questions you could ask to troubleshoot and solve this issue:
a) Does the code exist in the codes table (Board Level)?
b) Does the Course exist from the School Level?
c) Is this perhaps an expired code?
d) Did you fill out all the required fields on this screen (Fields marked with an asterisk *)
Solution:
First, make sure the code exists and that it 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 as a completed course and review the effective dates of that code.
4) It is possible that the code you are trying to add has expired?
Second, make sure the course exists from the school level.
School Level > Menu > Setup > Class Info > Course (This Year)
If you are still experiencing this issue after going through these solution steps, please let us know.