After applying 17.3 RU18, with a variety of different types of updates to a ticket, the error message "Field SET call_back_date has a bad date!" appears
The problem does not exist with new tickets created, only with tickets that existed before the 17.3 RU18 upgrade.
CA Service Desk Manager 17.3 RU18
Discovered that all the date fields in the ticket either had a valid date or had a "0".
Date fields should appear empty and contain a NULL in the MDB database instead of a "0".
After querying the MDB database, it was confirmed that all the unset dates on existing ticket records had somehow been reset from NULL to "0".
After running a SQL UPDATE statement to convert all the "0" dates back to NULL, there were no further problems making updates to the previous/old tickets.
Confirmed that the 17.3 RU18 upgrade would not have made that type of change in the MDB database, so some other user or action would have been responsible for this data change.