Bug 182284 Error message props up after previewing a report with a group on date type column
Use the attached rptdesign file preview Expected Result: Data is grouped without error message. Actual result: error message props up.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/group/GroupCalculatorFactory.java
{
	/**
	 * 
	 * @param interval
	 * @param dataType
	 * @param intervalStart
	 * @param intervalRange
	 * @return
	 * @throws DataException
	 */
	public static ICalculator getGroupCalculator( int interval, int dataType,
			Object intervalStart, double intervalRange ) throws DataException
	{
		if ( !isValidInterval( interval, dataType ) )