Hello everyone !
Here's the problem:

I have a JDesktopPane and I want to put two JInternalFrames in it.
Here's the piece of code:

getDesktopPanel().add(getPropsPane());
getDesktopPanel().add(getChildFrame());

At the first line the "illegal component position" exception is thrown

getDesktopPanel() returns a JDesktopPane. getPropsFrame() and
getChildFrame() both return JInternalFrames. What's wrong here ?!

Thanks for replying,
DAN