I have been having the same problem for a few weeks and sent an email for support and got nothing back. I then followed Lord of the Rings fixes and by deleting the limewire application data folder it now works perfectly. I recommend his thread for fixing this.
Cheers LOTR.

I have had Limewire for nearly a yeart and it was fne until last night when I tried to open it and got the "internal fatal error" message. I installed and uninstalled it countless times and tried loading the back up. Nothing works. I'm using (or was) Limewire 4.10. 9

This is the full error message:

LimeWire version 4.10.9
Java version 1.5.0_03 from Sun Microsystems Inc.
Windows XP v. 5.1 on x86
Free/total memory: 604576/9469952

FATAL ERROR!

java.lang.ExceptionInInitializerError
at com.limegroup.gnutella.RouterService.start(RouterS ervice.java:423)
at com.limegroup.gnutella.gui.Initializer.initialize( Initializer.java:300)
at com.limegroup.gnutella.gui.GUILoader.load(GUILoade r.java:41)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Nativ e Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknow n Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Un known Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.limegroup.gnutella.gui.Main.main(Main.java:44)
Caused by: java.lang.IllegalStateException: unread block data
at java.io.ObjectInputStream$BlockDataInputStream.set BlockDataMode(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.defaultReadFields(Unknow n Source)
at java.io.ObjectInputStream.readSerialData(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unkno wn Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at java.util.HashMap.readObject(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Nativ e Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknow n Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Un known Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at java.io.ObjectStreamClass.invokeReadObject(Unknown Source)
at java.io.ObjectInputStream.readSerialData(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unkno wn Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at com.limegroup.gnutella.spam.RatingTable.readData(R atingTable.java:214)
at com.limegroup.gnutella.spam.RatingTable.<init>(Rat ingTable.java:58)
at com.limegroup.gnutella.spam.RatingTable.<clinit>(R atingTable.java:34)
... 8 more


-- listing session information --
Current thread: main
Active Threads: 31
Uptime: 0:12
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: 1
Number of Active HTTP Downloaders: 0
Number of Waiting Downloads: 0
Received incoming this session: false
Number of Shared Files: 1
Guess Capable: false
Received Solicited UDP: true
SIMPP version: 48
Port Stable: false
FWT Capable: false
Last Reported Port: 11047
External Port: 41543
IP Pongs Received: 21

-- listing threads --
SavedFileLoader: 1
NIODispatcher: 1
Image Fetcher 2: 1
UDPHostRanker: 1
DownloadWorker: 1
main: 1
MulticastService: 1
Acceptor: 1
AWT-EventQueue-0: 1
AWT-Windows: 1
AWT-Shutdown: 1
Image Fetcher 1: 1
Timer-0: 1
Image Fetcher 0: 1
Image Fetcher 3: 1
IconLoader: 1
MessageDispatch: 1
ConnectionFetcher: 4
FileManagerLoader: 1
Thread-9: 1
DelayedGUI: 1
QueryUnicaster: 1
ManagedDownload: 1
Java2D Disposer: 1
TimerQueue: 1
QRPPropagator: 1
HTTPAcceptor: 1
UpdateHandler: 1


-- listing properties --
FILTER_HASH_QUERIES=true
APP_HEIGHT=728
FRACTIONAL_UPTIME=0.08899393
FILTER_VBS=false
LAST_EXPIRE_TIME=1148609812687
SESSIONS=8
LAST_ACCEPTABLE_BUG_VERSION=4.11.1
FILTER_ADULT=true
EVIL_HOSTS=BearShare 5.2
UPDATE_DOWNLOAD_DELAY=10000000
RUN_ONCE=true
COUNTRY=
MIN_CONNECT_TIME=7
CLIENT_ID=BF620A5AE823B136FA9CAC557B0B6800
LAST_SHUTDOWN_TIME=1149182151921
MAX_UPLOAD_BYTES_PER_SEC=28
IDLE_CONNECTIONS=2
PORT=41543
TOTAL_UPTIME=112278

Thanks for any help!!
AVERAGE_UPTIME=22455
UNSET_FIREWALLED_FROM_CONNECTBACK=true
RUN_ON_STARTUP=false
UPDATE_GIVEUP_FACTOR=24
FLUSH_DELAY_TIME=256
LAST_FWT_STATE=true
FILTER_WMV_ASF=false
PLAYER_ENABLED=false
INSTALLED=true
MAX_SIM_DOWNLOAD=8
LAST_GWEBCACHE_FETCH_TIME=1148609903515
CONNECTION_SPEED=350
MAX_DOWNLOAD_BYTES_PER_SEC=136
UPDATE_DELAY=252000020
WINDOW_X=113

You could try updating your Java to 1.5 update 6 and if that fails try the beta version...Make sure you get the JRE and install the offline version...