Java error in mailbox.log

[MGSteve]

Any idea as to what this is, I'm getting loads of these being logged.

java.lang.IllegalStateException: response  at org.mortbay.jetty.HttpConnection$RequestHandler.startResponse(HttpConnection.java:865)
        at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:403)
        at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:205)
        at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:381)
        at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:396)
        at org.mortbay.thread.BoundedThreadPool$PoolThread.run(BoundedThreadPool.java:442)

2009-04-07 19:47:31,169 ERROR [btpool0-91] [] log - handle failed
java.lang.IllegalStateException: response
        at org.mortbay.jetty.HttpConnection$RequestHandler.startResponse(HttpConnection.java:865)
        at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:403)
        at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:205)
        at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:381)
        at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:396)
        at org.mortbay.thread.BoundedThreadPool$PoolThread.run(BoundedThreadPool.java:442)