The transaction log file you specify in the WITH LOG IN clause must not already exist. The database server must start a log file fresh; it has no means of appending log data to an old log file. An existing log file contains recovery information that may be crucial, so it will not simply empty an existing file. To make a full backup, lock the database, copy all of the database directory to a backup medium, erase the log file (it is no longer needed), and use the START DATABASE statement. To make a partial backup, lock the database, copy the log file to a backup medium and store it with the full backup, erase or rename the log file, and use the START DATABASE statement.