Run under GTK L&F (using WinXP here), and go to
Tools | Import Management Tool.

Dafe, assigning to you initially, as the exception
occurs in your code, and I don't know what it
does.  It looks, though, like someone is trying to
show a null component.  Possibly someone else is
swallowing an exception?  (most likely some
UIDefaults related thing?)

Annotation: Exception occurred in Request Processor
java.lang.NullPointerException
        at
org.openide.util.AsyncInitSupport.<init>(AsyncInitSupport.java:56)
        at
org.openide.util.Utilities.attachInitJob(Utilities.java:2391)
        at
org.netbeans.modules.java.imptool.ImpToolExecutor.execute(ImpToolExecutor.j
ava:80)
        at
org.netbeans.modules.java.imptool.ImpToolAction.performAction(ImpToolAction
.java:41)
        at
org.openide.util.actions.NodeAction.performAction(NodeAction.java:193)
        at
org.openide.util.actions.CallableSystemAction$1.run(CallableSystemAction.ja
va:78)
        at
org.openide.util.actions.CallableSystemAction$2.run(CallableSystemAction.ja
va:121)
        at org.openide.util.Task.run(Task.java:136)
        at
org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:330)