...
    List<crimes> Crimes = new List<crimes>();
    DataTable crimesData = blablabla
    for(int i=0;i<crimesData.Rows.Count;i++)
    {
        crimes newcrime = new crimes(blablabla); // initiate new class with new parameters
        Crimes.Add(newcrime);
    }
    API.setEntitySyncedData(phandle,"Crimes",Crimes);
    ...

...
List<crimes> Crimes = (List<crimes>)API.getEntitySyncedData(player.handle,"Crimes"); // error
...

System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
  at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00038] in <8f2c484307284b51944a1a13a14c0266>:0