To log flights that do not include a Duration or SIM such as when flying as FE or logging ground school you can do the following:

1) Go to Options...Flight Log
2) Clear the checkbox next to FAR Error Checking
3) Clear the checkbox at the bottom of the dialog regarding auto-purge

You can now log flights as desired which will bypass Logbook Pro's minimum required columns of Date, Type, Ident, Route, and Duration (or SIM).  However, for items such as Route and Ident, we suggest at least entering N/A or SIM, etc. and not leaving these columns blank.