Hey all ! I'm trying to do an Advanced Intercompany Journal Entry import, but keep on getting the csv response error as "Accounts Receivable and Accounts Payable lines marked for elimination must specify an Intercompany Customer or Vendor". Any help ?

The error explains it pretty well. At least one of the accounts in your import is Accounts Payable or Accounts Receivable type and marked to eliminate. When that's the case, you need to specify an Interco Vendor or Customer on that line.