We received a Failed: CANNOT_UPDATE_CONVERTED_LEAD: cannot reference converted lead error recently. The person was a member of a program, synced to a SFDC campaign, and achieved the success criteria. Our inside sales team member converted the SFDC lead to a contact. In a later program, that same person was selected based on a smart list that included members of the previous program. The new program was active when we received the error.
Searching in SFDC, there is only one contact record for this person. In Marketo, there are two records: one with SFDC Type: Lead and one with SFDC Type: Contact. I was under the impression that, when a SFDC lead was converted into a contact, the Marketo person record followed.
Why would we have two records for the same person in Marketo in this instance?
Without knowing your Salesforce instance, I would hazard a guess that Marketo "lost track" of the lead on lead conversion. By that I mean during the lead conversion process there was a point where Marketo could no longer see the person/lead based on some kind of sharing rule or other permissions issue. Then something changed on the Contact so that Marketo could see it again, and it no longer recognises it as the existing lead, and hence created a "new" Contact because that's what it thinks Salesforce has done, created a new record.
I see this happen quite a bit when orgs have extremely complicated rules governing when Marketo can and can't see a record.