internal Error by using horizontalSplitPanel

Hello,

when using horizontalSplitPanel.setSplitPosition(750, Sizeable.UNITS_PIXELS); generates the applications a internal Error.

horizontalSplitPanel = new HorizontalSplitPanel();
        [b]horizontalSplitPanel.setSplitPosition(750, Sizeable.UNITS_PIXELS);[/b]
        horizontalSplitPanel.setLocked(false);
        horizontalSplitPanel.setHeight("450px");
        horizontalSplitPanel.setWidth("100%");
        addComponent(horizontalSplitPanel);

If I remove the line, the error no longer occurs.
Maybe someone has a tip, why this might be?

Thanks in advance

The problem has done himself.
Under Netbeans it is problem with the version of Vaadin, when both are in the lib folder.
Removing the old version, dissolves the problem.