Linking an Activity to a Sales Opportunity

CompanyService actCmp = Git_DIApi.VCmp.GetCompanyService();
ActivitiesService actService = (ActivitiesService)actCmp.GetBusinessService(ServiceTypes.ActivitiesService);
Activity act = (Activity)actService.GetDataInterface(ActivitiesServiceDataInterfaces.asActivity);

try
{   ActivityParams oParams;
    act.Activity = BoActivities.cn_Task;
    act.ActivityType = -1; //"1 Продажи"
    act.Subject = 50; //"Follow Up"
    act.CardCode = CardCode;

    act.ContactPersonCode = CntctCode;
    act.HandledBy = SlpCode;
    act.Notes = "";

    DateTime now = DateTime.Now;
    DateTime startDate = now.AddDays(3);
    DateTime endDate = now.AddDays(10);
    act.ActivityDate = now;
    act.ActivityTime = now;
    act.StartDate = startDate;
    act.StartTime = startDate;
    act.EndDuedate = endDate;
    act.EndTime = endDate;

    act.DocType = ObjTypeQt;
    act.DocEntry = DocId;

    act.SalesOpportunityId = OpprId; // ! Linking an Activity
    act.SalesOpportunityLine = Line; // !

    oParams = actService.AddActivity(act);
    int ActCode = oParams.ActivityCode;
}
catch(Exception ex)
{   BubbleEvent = false;
    errMsg = "Ошибка при добавлении активности: " + ex.Message;
}
finally
{   Marshal.ReleaseComObject(actCmp); actCmp = null;
    Marshal.ReleaseComObject(actService); actService = null;
    Marshal.ReleaseComObject(act); act = null;
}