HoriOrientPosition is supposed to be long, if you look here:
http://api.openoffice.org/docs/common/ref/com/sun/star/text/Shape.html#HoriOrientPosition
Type[long] HoriOrientPosition  (via .getPropertySetInfo())

But actually it's an Integer:
System.out.println(xFrameProps.getPropertyValue("HoriOrientPosition").getClass());
=> Integer

xFrameProps.setPropertyValue("HoriOrientPosition", new Integer(420));
=> works
xFrameProps.setPropertyValue("HoriOrientPosition", new Long(420));
=> com.sun.star.lang.IllegalArgumentException


Here is the code snippet:
XTextFrame xFrame = (XTextFrame) UnoRuntime.queryInterface (
           XTextFrame.class, xMSFDoc.createInstance (
                      "com.sun.star.text.TextFrame" ) );
XShape xShape = (XShape) UnoRuntime.queryInterface(XShape.class, xFrame);
XPropertySet xFrameProps = (XPropertySet)UnoRuntime.queryInterface(
                    XPropertySet.class, xFrame );
xFrameProps.setPropertyValue( "AnchorType", TextContentAnchorType.AT_PAGE );
xFrameProps.setPropertyValue( "HoriOrient", new Short(HoriOrientation.NONE));
System.out.println(xFrameProps.getPropertyValue("HoriOrientPosition").getClass());
xFrameProps.setPropertyValue("HoriOrientPosition", new Integer(420));