I've been serialising date_time stuff (ptimes to be specific). They weren't initialised when we were loading old files as they didn't containt the information, so when the file is saved in the new format, we get an entry in the XML archive: <ptime_date class_id="26" tracking_level="0" version="0"> <date>not-a-date-time</date> </ptime_date> <ptime_time_duration class_id="27" tracking_level="0" version="0"> <time_duration_hours>-1732919508</time_duration_hours> <time_duration_minutes>0</time_duration_minutes> <time_duration_seconds>22</time_duration_seconds> <time_duration_fractional_seconds>775806</time_duration_fractional_seconds> </ptime_time_duration> I realise 'not-a-date-time' is invalid, and would be happy if the serialise failed in both directions, but currently it succeeds to write it to an oarchive, but fails to read it from an iarchive. I don't mind which way we go (i.e. both valid or both invalid) but have oarchive working and iarchive failing isn't overly useful really. Thanks Russell