Wicket A child with id 'xxx' already exists- エラーについて

java.lang.IllegalArgumentException: A child with id '@@@@@@' already exists 

Wicket 1.5.2

    /**
     * Adds the child component(s) to this container.
     * 
     * @param children
     *            The child(ren) to add.
     * @throws IllegalArgumentException
     *             Thrown if a child with the same id is replaced by the add operation.
     * @return This
     */
    public MarkupContainer add(final Component... children)
    {
        for (Component child : children)
        {
            Args.notNull(child, "child");

            if (this == child)
            {
                throw new IllegalArgumentException(
                    exceptionMessage("Trying to add this component to itself."));
            }

            MarkupContainer parent = getParent();
            while (parent != null)
            {
                if (child == parent)
                {
                    String msg = "You can not add a component's parent as child to the component (loop): Component: " +
                        this.toString(false) + "; parent == child: " + parent.toString(false);

                    if (child instanceof Border.BorderBodyContainer)
                    {
                        msg += ". Please consider using Border.addToBorder(new " +
                            Classes.simpleName(this.getClass()) + "(\"" + this.getId() +
                            "\", ...) instead of add(...)";
                    }

                    throw new WicketRuntimeException(msg);
                }

                parent = parent.getParent();
            }

            checkHierarchyChange(child);

            if (log.isDebugEnabled())
            {
                log.debug("Add " + child.getId() + " to " + this);
            }

            // Add the child to my children
            Component previousChild = children_put(child);
            if (previousChild != null && previousChild != child)
            {
                throw new IllegalArgumentException(
                    exceptionMessage("A child '" + previousChild.getClass().getSimpleName() +
                        "' with id '" + child.getId() + "' already exists"));
            }

            addedComponent(child);

        }
        return this;
    }

        // Add the child to my children
        Component previousChild = children_put(child);
        if (previousChild != null && previousChild != child)
        {
            throw new IllegalArgumentException(
                exceptionMessage("A child '" + previousChild.getClass().getSimpleName() +
                    "' with id '" + child.getId() + "' already exists"));
        }