Bug 153506 Strange error message when group key refers to bad binding column name
Run attached report design. The following error is shown: Group key "groupkey" in group 1 cannot depend on column bindings defined in the group lower than itself. This is a strange error. Since the actual problem is that the table's binding column "groupkey" is defined to refer to another existing binding: row["bad"]. EXPECTED BEHAVIOR: The error message should clearly indicate that a non-existing binding is the cause of the failure.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/ExprManagerUtil.java
}
	}
	/**
	 * 
	 * @param startNode
	 * @param candidateNode
	 * @return
	 * @throws DataException 
	 */
	private void isValidNode( Node startNode, Node candidateNode ) throws DataException
	{
		
		Object[] nodes = startNode.getChildren( ).toArray( );
		for ( int i = 0; i < nodes.length; i++ )
		{
			if ( candidateNode.equals( nodes[i] )
					|| startNode.equals( nodes[i] ) )
			{
				throw new DataException( ResourceConstants.COLUMN_BINDING_CYCLE,((Node)nodes[i]).getValue( ));
			}
			else
			{
				isValidNode( (Node) nodes[i], candidateNode );
			}
		}
	}
	/**
	 * 
	 * @param source
	 * @return