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 GroupSpec.NO_INTERVAL :
				return true;
			case GroupSpec.NUMERIC_INTERVAL :
				if ( isNumber( dataType ) )
					return true;
				else
					throw new DataException( ResourceConstants.BAD_GROUP_INTERVAL_TYPE,
							new Object[]{
									"numeric", DataType.getName( dataType )
							} );
			case GroupSpec.STRING_PREFIX_INTERVAL :
				if ( isString( dataType ) )
					return true;
				else
					throw new DataException( ResourceConstants.BAD_GROUP_INTERVAL_TYPE,
							new Object[]{
									"string prefix",
									DataType.getName( dataType )
							} );
			default :
				if ( isDate( dataType ) )
					return true;
				else
					throw new DataException( ResourceConstants.BAD_GROUP_INTERVAL_TYPE,
							new Object[]{
									"date", DataType.getName( dataType )
							} );
		}
	}