The datalogger stores two types of records, detection and event records.  Detection records are tags appearing on the antenna and event records are exceptional events ("low battery").

If the datalogger encounters a record other than a detection or event record it will display the "bad type code" message.  These are an indication that the dataogger file has become corrupted.  The solution is to download all data and re-initialize the database file (Setup pane on the PDA or the FRD command).