When choosing to substitute a course to fulfill a specific requirement, you may receive the error message: "Error: Course has already been used in another substitution and cannot be used in additional substitution"
The same course, no matter what academic year it was taken (this applies to courses that are allowed to be taken multiple times for credit) cannot be used more than once in substitution to fulfill one specific requirement.
If you encounter this error message, the system is seeing that this same course has already been entered as a substitution for this specific requirement.
Review all of the courses entered under the Requirement heading to confirm that this course has already been used in substitution.