have you reported this to support?  Bugs reported directly to bugzilla go to 
the bottom of the priority queue. 
 
Can you run the nmbd daemon under valgrind, and report where it failed?  I've 
been completely unable to reproduce this problem here, so we're gonna have to 
debug this on your machine. 

*** Bug 172714 has been marked as a duplicate of this bug. ***

I haven't the faintest clue how to use valgrind properly... but took a quick 
look and have attached output from a run under script(1).
FYI - nmbd is running for maybe 30 seconds at a time right now.

Created attachment 120818 [details]
output from valgrind run

Opened new (Red Hat Contract) Service Request #720168

Upgraded to samba-3.0.20b-1 from www.samba.org (rebuilt from SRPM), seems to
have solved the problem.
Don't know why, don't have time to care.

We have been sorely bitten by this bug as well :-(
Our Microsoft Networking browse servers are exclusively Redhat RHEL3/4 servers.
We moved the SAMBA "wins server" (Domain Master Browser) function from an old
RHEL3 server to a new RHEL4-U2 (all patches installed) server
running samba-3.0.10-1.4E.2.
Immediately our Windows network browsing came to a grinding halt :-(

The last line seen in /var/log/samba/nmbd.log is:
*** glibc detected *** free(): invalid next size (fast): 0x09023558 ***
and although the nmbd process is still running, nmbd has ceased responding
to "smbclient -L <servername>".

This seems to be the same bug as reported in 150583 and 150582 almost one
year ago.

We're greatly surprised that such a fundamental bug in SAMBA functionality
(remember, we're an RHEL only shop, no MS-Windows servers here) has
been allowed to exist through several versions of RHEL4.

Could you please advise: Should we uninstall Redhat's SAMBA RPMs and 
switch to the SAMBA 3.0.21b RPM from samba.org (and become responsible ourselves
for updating SAMBA manually), or can we expect a timely bug fix from Redhat ?

I also reported this on Bug 150582, but that bug was unfortunately closed.

Using samba-3.0.10-1.4E.2

i can get around this error via switching off "wins proxy" - however i need its
functionality.

And i can verify that upgrading to samba.org packages helps.

We got tired of waiting for Redhat to fix the Samba bug in RHEL4, and we *need* a 
working Samba WINS server, so we decided to uninstall the Redhat Samba RPMs and 
build our own from samba.org's samba-3.0.21b source.

In the Samba source tree we go to packaging/RHEL and run makerpms.sh
in order to build drop-in replacements for the Redhat RPMs.

We can now report that samba-3.0.21b works without a glitch as a WINS server
for multiple networks.

Created attachment 143502 [details]
nmbd crash / stales.

Could you please try this patch ?
It did solve the issue for one of our customers having the very same traces you
got on this wins proxy problem.

*sigh*
We had to give up on the RHEL RPM packages a *long* time ago, and went with 
compiled source from the Samba project.
We just can't wait that long for a critical problem.
So, no, I actually can't test the patch.  Sorry...

This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux maintenance release.  Product Management has requested
further review of this request by Red Hat Engineering, for potential
inclusion in a Red Hat Enterprise Linux Update release for currently deployed
products.  This request is not yet committed for inclusion in an Update
release.

lol - and in the next 2 years - it is gonna be fixed!

https://bugzilla.samba.org/show_bug.cgi?id=2215

*** Bug 229801 has been marked as a duplicate of this bug. ***

An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHEA-2007-0698.html