OK, back to the original bug report by Gary Weinfurther. In his .bzr.log I see the regular error pattern:


Tue 2010-11-23 10:31:39 -0500
0.063  bazaar version: 2.2.1
0.063  bzr arguments: [u'qsubprocess', u'--bencode', u'l6:commit2:-m17:added search icon31:public_html/img/search-icon.pnge']
0.063  looking for plugins in C:/Users/Gary/AppData/Roaming/bazaar/2.0/plugins
0.063  looking for plugins in C:/Program Files (x86)/Bazaar/plugins
0.156  encoding stdout as osutils.get_user_encoding() 'cp1252'
0.203  bazaar version: 2.2.1
0.203  bzr arguments: [u'commit', u'-m', u'added search icon', u'public_html/img/search-icon.png']
0.203  encoding stdout as osutils.get_user_encoding() 'cp1252'
0.281  opening working tree 'D:/Projects/Lincoln/Digital Frontline/2010-11/web/source'
2.730  Traceback (most recent call last):
  File "bzrlib\commands.pyo", line 912, in exception_to_return_code
  File "bzrlib\commands.pyo", line 1112, in run_bzr
  File "bzrlib\commands.pyo", line 690, in run_argv_aliases
  File "bzrlib\commands.pyo", line 705, in run
  File "bzrlib\cleanup.pyo", line 135, in run_simple
  File "bzrlib\cleanup.pyo", line 165, in _do_with_cleanups
  File "C:/Program Files (x86)/Bazaar/plugins\qbzr\lib\commands.py", line 767, in run
  File "C:/Program Files (x86)/Bazaar/plugins\qbzr\lib\subprocess.py", line 888, in run_subprocess_command
  File "bzrlib\commands.pyo", line 1112, in run_bzr
  File "bzrlib\commands.pyo", line 690, in run_argv_aliases
  File "bzrlib\commands.pyo", line 705, in run
  File "bzrlib\cleanup.pyo", line 135, in run_simple
  File "bzrlib\cleanup.pyo", line 165, in _do_with_cleanups
  File "bzrlib\builtins.pyo", line 3200, in run
  File "bzrlib\decorators.pyo", line 192, in write_locked
  File "bzrlib\workingtree_4.pyo", line 629, in lock_write
  File "bzrlib\branch.pyo", line 2452, in lock_write
  File "bzrlib\lockable_files.pyo", line 187, in lock_write
  File "bzrlib\lockdir.pyo", line 648, in lock_write
  File "bzrlib\lockdir.pyo", line 563, in wait_lock
  File "bzrlib\lockdir.pyo", line 524, in attempt_lock
  File "bzrlib\lockdir.pyo", line 254, in _attempt_lock
LockFailed: Cannot lock LockDir(file:///L:/IPD/Lincoln/Digital%20Frontline/2010-11/web/source/branch-php/.bzr/branch/lock): lock was renamed into place, but now is missing!

2.730  Transferred: 0kB (0.0kB/s r:0kB w:0kB)
2.730  return code 3
[ 4996] 2010-11-23 10:32:32.572 WARNING: Cannot save commit data because the branch is locked.
[ 4996] 2010-11-23 10:32:32.572 WARNING: Cannot save commit data because the branch is locked.
7395.142  opening working tree 'D:/Projects/Lincoln/Digital Frontline/2010-11/web/source'
60.514  None

The first part comes from `bzr commit` that we run as subprocess. Therefore this problem should be repeatable with command-line `bzr commit`. If it's not I'd like to see other .bzr.logs

The second part, specifically 
 WARNING: Cannot save commit data because the branch is locked.
that's from qcommit trying to update commit_data in branch.conf.
This warning could be triggered only from

    def save_commit_data(self):
        if (self.tree.branch.control_files.get_physical_lock_status()
            or self.tree.branch.is_locked()):
            # XXX maybe show this in a GUI MessageBox (information box)???
            from bzrlib.trace import warning
            warning("Cannot save commit data because the branch is locked.")
            return

And after the warning we did return, so even did not trying to update branch.conf. I have no idea why the warning messages is doubled in the .bzr.log. Do you? But actually that means underlying `bzr commit` running in the subprocess is failing due locking problems.

Please, if you still can reproduce this issue, please attach here your own .bzr.log (relevant part of it, or just a tail after you get that error). Also, please check do you have any anti-virus monitor software running that make real-time check of the filesystem?