When I update from Netbeans 5.5 to 6.0, I can't start the emulator for J2ME development anymore. Later I've found that the problem is that Netbeans 6.0 is bundled with WTK(Wireless ToolKits) 2.5.2, whereas the 5.5 uses WTK 2.2. Then I go to the menu "Tools"->"java platforms" and remove the WTK 2.2. After removal, you'll see the project icons using J2ME show some errors in the "Project Navigator" view. Don't panic. Just go to the "Project Properties" dialog to ensure the "Emulator Platform" is WTK 2.5.2. Click OK button and you're done!