I have the same bug when I want to run any java programs (netbeans 5.5 ; netbeans 6 ; java web start )
I am on hardy upgraded from a feisty. sun-java6 is installed

Runing java web start
petit@petit-laptop-L:~$ /usr/lib/jvm/java-6-sun-1.6.0.04/bin/javaws -verbose -viewer
Java(TM) Web Start 1.6.0_04 Launching: /usr/lib/jvm/java-6-sun-1.6.0.04/jre/bin/java
/usr/lib/jvm/java-6-sun-1.6.0.04/jre/bin/java
 -Xbootclasspath/a:/usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/javaws.jar:/usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/deploy.jar
 -classpath
 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/deploy.jar
 -Djava.security.policy=file:/usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/security/javaws.policy
 -DtrustProxy=true
 -Xverify:remote
 -Djnlpx.home=/usr/lib/jvm/java-6-sun-1.6.0.04/jre/bin
 -Djnlpx.jvm=/usr/lib/jvm/java-6-sun-1.6.0.04/jre/bin/java
 com.sun.javaws.Main
 -viewer
 
petit@petit-laptop-L:~$ Locking assertion failure.  Backtrace:
#0 /usr/lib/libxcb-xlib.so.0 [0xb4bc3767]
#1 /usr/lib/libxcb-xlib.so.0(xcb_xlib_unlock+0x31) [0xb4bc38b1]
#2 /usr/lib/libX11.so.6(_XReply+0xfd) [0x9068f29d]
#3 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0x90a3f8ce]
#4 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0x90a1c067]
#5 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0x90a1c318]
#6 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so(Java_sun_awt_X11GraphicsEnvironment_initDisplay+0x2f) [0x90a1c61f]
#7 [0xb4c943aa]
#8 [0xb4c8cf0d]
#9 [0xb4c8cf0d]
#10 [0xb4c8a249]
#11 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/server/libjvm.so [0x637338d]
#12 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/server/libjvm.so [0x64fd168]
#13 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/server/libjvm.so [0x6373220]
#14 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/server/libjvm.so(JVM_DoPrivileged+0x363) [0x63c90d3]
#15 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/libjava.so(Java_java_security_AccessController_doPrivileged__Ljava_security_PrivilegedAction_2+0x3d) [0xb7ca596d]
#16 [0xb4c943aa]
#17 [0xb4c8cda7]
#18 [0xb4c8a249]
#19 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/server/libjvm.so [0x637338d]
java: xcb_xlib.c:82: xcb_xlib_unlock: Assertion `c->xlib.lock' failed.

petit@petit-laptop-L:~$ 


Runing netbeans 6 :
petit@petit-laptop-L:~$ /opt/netbeans/netbeans6/bin/netbeans 
Locking assertion failure.  Backtrace:
#0 /usr/lib/libxcb-xlib.so.0 [0xb4390767]
#1 /usr/lib/libxcb-xlib.so.0(xcb_xlib_unlock+0x31) [0xb43908b1]
#2 /usr/lib/libX11.so.6(_XReply+0xfd) [0xb43e529d]
#3 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0xb44e88ce]
#4 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0xb44c5067]
#5 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0xb44c5318]
#6 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so(Java_sun_awt_X11GraphicsEnvironment_initDisplay+0x2f) [0xb44c561f]
#7 [0xb5b5eecd]
#8 [0xb5b57edd]
#9 [0xb5b57edd]
#10 [0xb5b55249]
#11 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/client/libjvm.so [0x621c40d]
#12 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/client/libjvm.so [0x6310378]
#13 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/client/libjvm.so [0x621c2a0]
#14 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/client/libjvm.so(JVM_DoPrivileged+0x363) [0x6272153]
#15 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/libjava.so(Java_java_security_AccessController_doPrivileged__Ljava_security_PrivilegedAction_2+0x3d) [0xb7b7096d]
#16 [0xb5b5eecd]
#17 [0xb5b57d77]
#18 [0xb5b55249]
#19 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/client/libjvm.so [0x621c40d]
java: xcb_xlib.c:82: xcb_xlib_unlock: Assertion `c->xlib.lock' failed.
/opt/netbeans/netbeans6/bin/../platform7/lib/nbexec: line 440: 14789 Abandon                 (core dumped) "/usr/lib/jvm/java-6-sun/bin/java" -Djdk.home="/usr/lib/jvm/java-6-sun" -classpath "/opt/netbeans/netbeans6/platform7/lib/boot.jar:/opt/netbeans/netbeans6/platform7/lib/org-openide-modules.jar:/opt/netbeans/netbeans6/platform7/lib/org-openide-util.jar:/usr/lib/jvm/java-6-sun/lib/dt.jar:/usr/lib/jvm/java-6-sun/lib/tools.jar" -Dnetbeans.system_http_proxy="DIRECT" -Dnetbeans.system_http_non_proxy_hosts="" -Dnetbeans.dirs="/opt/netbeans/netbeans6/nb6.0:/opt/netbeans/netbeans6/ide8:/opt/netbeans/netbeans6/java1:/opt/netbeans/netbeans6/apisupport1:/opt/netbeans/netbeans6/profiler2:/opt/netbeans/netbeans6/uml4:/opt/netbeans/netbeans6/harness:/opt/netbeans/netbeans6/cnd1:" -Dnetbeans.home="/opt/netbeans/netbeans6/platform7" '-Dnetbeans.importclass=org.netbeans.upgrade.AutoUpgrade' '-Dnetbeans.accept_license_class=org.netbeans.license.AcceptLicense' '-Xmx363m' '-Dorg.netbeans.modules.tomcat.autoregister.token=1196799232067' '-Dorg.netbeans.modules.tomcat.autoregister.catalinaHome=/opt/netbeans/apache-tomcat-6.0.14' '-Dcom.sun.aas.installRoot=/opt/netbeans/glassfish-v2' '-client' '-Xss2m' '-Xms32m' '-XX:PermSize=32m' '-XX:MaxPermSize=200m' '-Xverify:none' '-Dapple.laf.useScreenMenuBar=true' org.netbeans.Main --userdir "/home/petit/.netbeans/6.0" "--branding" "nb"
petit@petit-laptop-L:~$ 

Runing java console : 
petit@petit-laptop-L:~$ /usr/lib/jvm/java-6-sun-1.6.0.04/bin/jconsole
Locking assertion failure.  Backtrace:
#0 /usr/lib/libxcb-xlib.so.0 [0xb4c20767]
#1 /usr/lib/libxcb-xlib.so.0(xcb_xlib_unlock+0x31) [0xb4c208b1]
#2 /usr/lib/libX11.so.6(_XReply+0xfd) [0x906fa29d]
#3 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0x907fd8ce]
#4 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0x907da067]
#5 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so [0x907da318]
#6 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/xawt/libmawt.so(Java_sun_awt_X11GraphicsEnvironment_initDisplay+0x2f) [0x907da61f]
#7 [0xb4cf73aa]
#8 [0xb4ceff0d]
#9 [0xb4ceff0d]
#10 [0xb4ced249]
#11 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/server/libjvm.so [0x637338d]
#12 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/server/libjvm.so [0x64fd168]
#13 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/server/libjvm.so [0x6373220]
#14 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/server/libjvm.so(JVM_DoPrivileged+0x363) [0x63c90d3]
#15 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/libjava.so(Java_java_security_AccessController_doPrivileged__Ljava_security_PrivilegedAction_2+0x3d) [0xb7d0896d]
#16 [0xb4cf73aa]
#17 [0xb4cefda7]
#18 [0xb4ced249]
#19 /usr/lib/jvm/java-6-sun-1.6.0.04/jre/lib/i386/server/libjvm.so [0x637338d]
jconsole: xcb_xlib.c:82: xcb_xlib_unlock: Assertion `c->xlib.lock' failed.
Abandon (core dumped)
petit@petit-laptop-L:~$