java crashed with signal 5 in _XError()

I was debugging an application on NetBeans when the application suddenly froze. When stopped the debugger NetBeans froze and then just the application crashed showing this error

ProblemType: Crash
Architecture: amd64
CheckboxSubmission: f1b15b20a09c88034055ebde1ac7d6a2
CheckboxSystem: d00f84de8a555815fa1c4660280da308
Date: Mon Feb 15 12:13:30 2010
DistroRelease: Ubuntu 10.04
ExecutablePath: /usr/lib/jvm/java-6-openjdk/jre/bin/java
InstallationMedia: Ubuntu 9.10 "Karmic Koala" - Release amd64 (20091027)
NonfreeKernelModules: nvidia
Package: openjdk-6-jre-headless 6b17-1.7-1ubuntu1
ProcCmdline: /usr/lib/jvm/java-6-openjdk/bin/java -Xdebug -Xrunjdwp:transport=dt_socket,address=username-laptop:44101 -Dfile.encoding=UTF-8 -Xmx512m -classpath /home/username/NetBeansProjects/secureSWF_Compress/build/classes:/home/username/NetBeansProjects/secureSWF_Compress/src:/home/username/NetBeansProjects/secureSWF/build/classes:/home/username/NetBeansProjects/trunk/src:/home/username/NetBeansProjects/trunk/utilities:/home/username/NetBeansProjects/secureSWF_GUI/lib/swing-app-framework/appframework-1.0.3.jar:/home/username/NetBeansProjects/secureSWF_GUI/lib/swing-app-framework/swing-worker-1.1.jar:/home/username/NetBeansProjects/secureSWF_GUI/lib/swing-layout/swing-layout-1.0.4.jar:/home/username/NetBeansProjects/secureSWF_GUI/lib/ant.jar:/home/username/NetBeansProjects/secureSWF_GUI/lib/iText-2.1.5.jar:/home/username/NetBeansProjects/secureSWF_GUI/build/classes:/home/username/NetBeansProjects/secureSWF_GUI/src secureSWF.gui.SecureSwf
ProcEnviron:
 SHELL=/bin/bash
 LANG=en_US.utf8
ProcVersionSignature: Ubuntu 2.6.32-13.18-generic
Signal: 5
SourcePackage: openjdk-6
StacktraceTop:
 ?? () from /usr/lib/libgdk-x11-2.0.so.0
 _XError () from /usr/lib/libX11.so.6
 _XReply () from /usr/lib/libX11.so.6
 XShmGetImage () from /usr/lib/libXext.so.6
 ?? ()
Title: java crashed with signal 5 in _XError()
Uname: Linux 2.6.32-13-generic x86_64
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare