void SetGYearMonth(short year, byte month)
  Property Description  
    Argument year year sets the Year part of the date. (Valid Range = -9999 to 9999)  
    Argument month month sets the Month part of the date. Jan = 1, Feb = 2 etc. (Valid Range = 1 to 12)  
    Description Populates this CDateTime as type gYearMonth.  
    Remarks Throws: LtInvalidValueException thrown on parsing invalid values.
Throws: LtInvalidStateException thrown if this DateTimes current type is not either zeroYear or gMonth.