Customer created a Constituent List in BBIS with 46 records. They used that list for an email and 2 people on that list received the email twice. Both individuals had 2 BBIS accounts at one time and both of these accounts were linked to the same CRM record after a constituent merge in CRM. The customer deleted one of the BBIS records, so at the time of this email send, they only each had 1 active account.
Download and install the latest patch, which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.