DAL C# error 'cannot implicitly convert type'

public List<BOL.MonthlyEvent> List(string subsidiary_cd,string costcenter)
{
    oConnection.ConnectionString = ConnectionString;
    oConnection.Open();
    BOL.MonthlyEvent MEvent = new BOL.MonthlyEvent();
    SqlCommand oCommand = new SqlCommand();
    oCommand.Connection = oConnection;
    oCommand.CommandType = CommandType.StoredProcedure;
    oCommand.CommandText = "Monthly_Event_LIST1";
    oCommand.Parameters.Add(new SqlParameter("@SUBS_CD", subsidiary_cd));
    oCommand.Parameters.Add(new SqlParameter("@CostCenter", costcenter));
    SqlDataReader oReader = oCommand.ExecuteReader();
    while (oReader.Read())
    {

        if (oReader["Event_Date"].ToString() == "") { Event.EventDate = null; } else { MEvent.EventDate = Convert.ToDateTime(oReader["Event_Date"].ToString()); }
        MEvent.EventTitle = oReader.IsDBNull(oReader.GetOrdinal("EventTitle")) ? "" : oReader["EventTitle"].ToString();
        MEvent.EventDescription = oReader.IsDBNull(oReader.GetOrdinal("Event_Description")) ? "" : oReader["Event_Description"].ToString();
    }
    oReader.Close();
    oConnection.Close();
    return MEvent;
}

cannot implicitly convert type'BOL.MonthlyEvent' to 'system.collections.generic.list<BOL.MonthlyEvent>'