Duplicate Source Code Error

[kaldrich]

My org is starting to use the Campaign Segmentation Wizard but when we try to actually create the segments, we get an error message about a duplicate source code: "There was an error creating the segment Campaigns: Insert failed. First exception on row 1; first error: DUPLICATE_VALUE, duplicate value found: Source_Code__c duplicates value on record with id: 7012J000001BTbk: []"

I can't seem to find a validation rule regarding the source code. We do have an Apex Trigger TDTM_Campaign that's part of the NPSP (Nonprofit Success Pack). But I can't edit that apex code because it's managed.

Is it possible to make the segmentation wizard assign a new Source Code to avoid this error?