Problem occurs on Mac OS X (10.6.3) when trying to commit to a repository-- 
see transcript below-- MacBookPro CoreDuo

Nitro:SMBFW wayne$ hg commit -u "wcontello" -m "Version 3.1s-- code from TI"
transaction abort!
rollback completed
** unknown exception encountered, details follow
** report bug details to http://mercurial.selenic.com/bts/
** or mercurial@selenic.com
** Mercurial Distributed SCM (version 1.5.2+20100502)
** Extensions loaded: 
Traceback (most recent call last):
  File "/usr/local/bin/hg", line 27, in <module>
    mercurial.dispatch.run()
  File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 16, 
in run
    sys.exit(dispatch(sys.argv[1:]))
  File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 30, 
in dispatch
    return _runcatch(u, args)
  File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 50, 
in _runcatch
    return _dispatch(ui, args)
  File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 470, 
in _dispatch
    return runcommand(lui, repo, cmd, fullargs, ui, options, d)
  File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 340, 
in runcommand
    ret = _runcommand(ui, options, cmd, d)
  File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 521, 
in _runcommand
    return checkargs()
  File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 475, 
in checkargs
    return cmdfunc()
  File "/Library/Python/2.6/site-packages/mercurial/dispatch.py", line 469, 
in <lambda>
    d = lambda: util.checksignature(func)(ui, *args, **cmdoptions)
  File "/Library/Python/2.6/site-packages/mercurial/util.py", line 401, in 
check
    return func(*args, **kwargs)
  File "/Library/Python/2.6/site-packages/mercurial/commands.py", line 712, 
in commit
    node = cmdutil.commit(ui, repo, commitfunc, pats, opts)
  File "/Library/Python/2.6/site-packages/mercurial/cmdutil.py", line 1151, 
in commit
    return commitfunc(ui, repo, message, match(repo, pats, opts), opts)
  File "/Library/Python/2.6/site-packages/mercurial/commands.py", line 710, 
in commitfunc
    editor=e, extra=extra)
  File "/Library/Python/2.6/site-packages/mercurial/localrepo.py", line 858, 
in commit
    ret = self.commitctx(cctx, True)
  File "/Library/Python/2.6/site-packages/mercurial/localrepo.py", line 906, 
in commitctx
    m1.set(f, fctx.flags())
  File "/Library/Python/2.6/site-packages/mercurial/context.py", line 304, 
in flags
    return self._changectx.flags(self._path)
  File "/Library/Python/2.6/site-packages/mercurial/context.py", line 694, 
in flags
    flag = findflag(self._parents[0])
  File "/Library/Python/2.6/site-packages/mercurial/context.py", line 690, 
in findflag
    return ff(path)
  File "/Library/Python/2.6/site-packages/mercurial/dirstate.py", line 145, 
in f
    if 'x' in fallback(x):
TypeError: argument of type 'NoneType' is not iterable