In question of your problem, your db4o.persist has errors (as mentioned in log). A .persist file consists at least in two parts, the strategies and items:
Strategies { // must be the first part of the file, not optional
everyMinute : "0 * * * * ?" //or any other useful definition, this is maybe optional
default = everyMinute //at least a default strategy is required, but this could even be
// default = everyChange, restoreOnStartup
}
Items {
Lueftung_Auto_Mode : strategy = everyChange, restoreOnStartup //stretegy is optional...
Lueftung_Aussentemperatur_Message : strategy = everyChange, restoreOnStartup
Lueftung_Innentemperatur_Message : strategy = everyChange, restoreOnStartup
Lueftung_Ventilator_Message : strategy = everyChange, restoreOnStartup
Lueftung_Filterlaufzeit_Message : strategy = everyChange, restoreOnStartup
Lueftung_Status_Message : strategy = everyChange, restoreOnStartup
Lueftung_Fan_Level : strategy = everyChange, restoreOnStartup
}