Customer had a core file and the internal error from the hs_err file wasn't seen before:
  Internal Error (53594E4348524F4E495A45520E43505005B8)

The core file and Error Logs are at : 
/net/cores.central/cores/dir33/831603/CBOE_HTS_Core_20080122_pid20513.tar
/net/cores.central/cores/dir33/831603/hs_err_pid20513.log


Libraries from the machine where crash was seen : 
/net/cores.central/cores/dir33/831603/pkg_java_core.java.20513.1201008837.tar.Z


Customer has informed that this was seen in production.
Hence need to look at this to prevent future such cores.

JDK Version : 1.6.0_01-b06
Platform : x86
Operating System : Solaris 10


Analysis So Far :
===================

Here is where it failed :

This failed in monitor synchronizaton code:
void ObjectSynchronizer::deflate_idle_monitors() {
.....
    // Normal case ... The monitor is associated with obj.
    guarantee (obj->mark() == markOopDesc::encode(mid), "invariant") ;  <----- failed here
    if (mid->is_busy()) {
       if (ClearResponsibleAtSTW) mid->_Responsible = NULL ;
       nInuse ++ ;

This looks like similar to bug 6550161.
Need to look at this issue further in detail.