The server just disconnected on its own - I did not restart either the master or the slave. After that it refuses to connect. I have two other Windows XP slaves that are connected just fine. I tried both JNLP via JavaWS & headless connections. Same problem

Not sure how you would repeat the issue since I don't even know how it started. This is the output when I start it headless (just did this to see what errors there were):

Jul 22, 2010 9:01:09 AM hudson.remoting.jnlp.Main$CuiListener <init>
INFO: Hudson agent is running in headless mode.
Jul 22, 2010 9:01:09 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Locating server among http://149.244.178.189:8080/
Jul 22, 2010 9:01:09 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Connecting to 149.244.178.189:49311
Jul 22, 2010 9:01:09 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Handshaking
Jul 22, 2010 9:01:09 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Connected
Jul 22, 2010 9:01:09 AM hudson.remoting.Channel$ReaderThread run
SEVERE: I/O error in channel channel
java.io.IOException: Unexpected termination of the channel
at hudson.remoting.Channel$ReaderThread.run(Channel.java:875)
Caused by: java.io.EOFException
at java.io.ObjectInputStream$BlockDataInputStream.peekByte(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at hudson.remoting.Channel$ReaderThread.run(Channel.java:869)
Jul 22, 2010 9:01:09 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Terminated

and this repeats over and over.