I've got EXACTLY the same problem, i haven't changed anything since limewire decided to not work :S I've tried uninstalling, re-installing to no avail.

LimeWire version 4.8.1
Java version 1.5.0_02 from Sun Microsystems Inc.
Windows XP v. 5.1 on x86
Free/total memory: 627336/5566464

java.lang.NullPointerException
at javax.swing.BoxLayout.preferredLayoutSize(Unknown Source)
at java.awt.Container.preferredSize(Unknown Source)
at java.awt.Container.getPreferredSize(Unknown Source)
at javax.swing.JComponent.getPreferredSize(Unknown Source)
at java.awt.GridBagLayout.GetLayoutInfo(Unknown Source)
at java.awt.GridBagLayout.getLayoutInfo(Unknown Source)
at java.awt.GridBagLayout.ArrangeGrid(Unknown Source)
at java.awt.GridBagLayout.arrangeGrid(Unknown Source)
at java.awt.GridBagLayout.layoutContainer(Unknown Source)
at java.awt.Container.layout(Unknown Source)
at java.awt.Container.doLayout(Unknown Source)
at java.awt.Container.validateTree(Unknown Source)
at java.awt.Container.validate(Unknown Source)
at com.limegroup.gnutella.gui.GUIMediator$2.run(GUIMe diator.java:336)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForHierar chy(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarch y(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarch y(Unknown Source)
at java.awt.Dialog$1.run(Unknown Source)
at java.awt.Dialog.show(Unknown Source)
at java.awt.Component.show(Unknown Source)
at java.awt.Component.setVisible(Unknown Source)
at com.limegroup.gnutella.gui.UpgradeWindow.showProDi alog(UpgradeWindow.java:216)
at com.limegroup.gnutella.gui.GUIMediator.showDialogs ForFirstVisibility(GUIMediator.java:363)
at com.limegroup.gnutella.gui.GUIMediator.access$100( GUIMediator.java:69)
at com.limegroup.gnutella.gui.GUIMediator$3.run(GUIMe diator.java:350)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForHierar chy(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarch y(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)


Detail: Uncaught event-thread error.

-- listing session information --
Current thread: AWT-EventQueue-0
Active Threads: 16
Uptime: 0:04
Is Connected: false
Number of Ultrapeer -> Ultrapeer Connections: 0
Number of Ultrapeer -> Leaf Connections: 0
Number of Leaf -> Ultrapeer Connections: 0
Number of Old Connections: 0
Acting as Ultrapeer: false
Acting as Shielded Leaf: false
Number of Active Uploads: 0
Number of Queued Uploads: 0
Number of Active Managed Downloads: 0
Number of Active HTTP Downloaders: 0
Number of Waiting Downloads: 0
Received incoming this session: false
Number of Shared Files: 0
Guess Capable: false
Received Solicited UDP: false
SIMPP version: 3
Port Stable: true
FWT Capable: false
Last Reported Port: 6346
External Port: 6346
IP Pongs Received: 0

-- listing threads --
Image Fetcher 3: 1
QueryDispatcher: 1
IconLoader: 1
Image Fetcher 2: 1
Java2D Disposer: 1
TimerQueue: 1
Thread-8: 1
main: 1
MulticastService: 1
AWT-Shutdown: 1
AWT-Windows: 1
AWT-EventQueue-0: 1
QRPPropagator: 1
Image Fetcher 1: 1
Timer-0: 1
Image Fetcher 0: 1


-- listing properties --
INSTALLED=true
COUNTRY=
LAST_EXPIRE_TIME=1113858204405
CONNECTION_SPEED=1000
CLIENT_ID=4077034320D5E89D19806CD1A2C9E200


I've deleted the .Limewire folder, redownloaded java and limewire. Still no luck