This is because a student a contract is being recorded for has more than one alumni affiliation. To find the student, either record contracts in small batches to see where the problem is, or check each alumni affiliation to see if there are duplicates:
  1. Core
  2. Users/Access
  3. Profile
  4. Search the student
  5. Click Alumni Affiliation under System Information
If there is more than one alumni affiliation, one will need to be deleted in order to successfully record contracts in bulk for that student.

In order to find which students have more than one alumni affiliation, once you've identified the Grad Year(s) that won't record contracts, create the following advanced list:

Objects:
  • User Base (From the Constituent Information category)
    • School Class User (From the Graduation Class category)
      • Role Class User (From the Graduation Class category)

Display fields:
User Base.User ID
User Base.First Name
User Base.Last Name
User base.Grad Year
Role School Class.Grad Year

Global Filters:
Where - User Base.Grad Year - any of (select the effected Grad Years)

After creating this list, export to excel and use excels Highlight Duplicates function on the User ID column to identify the users with multiple Alumni Affiliations.