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
case IGroupDefinition.NUMERIC_INTERVAL :
					return new NumericGroupCalculator( intervalStart,
							intervalRange );
				case IGroupDefinition.STRING_PREFIX_INTERVAL :
					return new StringGroupCalculator( intervalStart,
							intervalRange );
				default :
					throw new DataException( ResourceConstants.BAD_GROUP_INTERVAL_INVALID );
			}
		}
		catch ( BirtException be )
		{
			throw DataException.wrap( be );
		}
	}
	/**
	 * 
	 * @param interval
	 * @param dataType
	 * @return
	 * @throws DataException
	 */
	private static boolean isValidInterval( int interval, int dataType )
			throws DataException
	{
		if ( dataType == DataType.ANY_TYPE || dataType == DataType.UNKNOWN_TYPE )
		{
			return true;
		}
		switch ( interval )