Explorer does not open anymore

Just until today, Bazaar Explorer worked fine on my Windows 7 machine.
Now it does not open anymore all of a sudden.

I have uninstalled and reinstalled the 2.5.1 Standalone Version of bazaar. I am also using Cygwin, and have Bazaar and Python also installed in Cygwin, maybe this is causing conflicts? Here are the contents of the log:

Thu 2012-06-14 18:49:36 +0200
0.078 bazaar version: 2.5.1
0.078 bzr arguments: [u'explorer']
0.078 looking for plugins in C:/Users/tommi/AppData/Roaming/bazaar/2.0/plugins
0.078 looking for plugins in C:/Program Files/Entwicklung/Bazaar/plugins
0.172 encoding stdout as osutils.get_user_encoding() 'cp1252'
0.375 Deprecated function called
Called from:
  File "bzrlib\lazy_import.pyo", line 200, in _import
  File "C:/Program Files/Entwicklung/Bazaar/plugins\explorer\lib\explorer.py", line 32, in <module>
  File "C:/Program Files/Entwicklung/Bazaar/plugins\explorer\lib\desktop_env.py", line 158, in <module>
0.609 Deprecated method called
Called from:
  File "C:/Program Files/Entwicklung/Bazaar/plugins\explorer\lib\explorer.py", line 166, in __init__
  File "C:/Program Files/Entwicklung/Bazaar/plugins\explorer\lib\explorer.py", line 258, in _refresh_user_configuration
  File "C:/Program Files/Entwicklung/Bazaar/plugins\explorer\lib\explorer.py", line 265, in get_default_editor
0.609 loading explorer extensions for clothes ['Bazaar support', 'Register on Launchpad']
0.609 explorer extensions provided by the colo plugin in C:/Program Files/Entwicklung/Bazaar/plugins/colo/explorer
0.656 Traceback (most recent call last):
  File "bzrlib\commands.pyo", line 920, in exception_to_return_code
  File "bzrlib\commands.pyo", line 1131, in run_bzr
  File "bzrlib\commands.pyo", line 673, in run_argv_aliases
  File "bzrlib\commands.pyo", line 695, in run
  File "bzrlib\cleanup.pyo", line 136, in run_simple
  File "bzrlib\cleanup.pyo", line 166, in _do_with_cleanups
  File "C:/Program Files/Entwicklung/Bazaar/plugins\explorer\lib\commands.py", line 162, in run
  File "C:/Program Files/Entwicklung/Bazaar/plugins\explorer\lib\explorer.py", line 208, in __init__
  File "C:/Program Files/Entwicklung/Bazaar/plugins\explorer\lib\wt_browser.py", line 49, in __init__
  File "C:/Program Files/Entwicklung/Bazaar/plugins\explorer\lib\wt_browser.py", line 450, in __init__
  File "C:/Program Files/Entwicklung/Bazaar/plugins\explorer\lib\wt_browser.py", line 685, in __init__
  File "C:/Program Files/Entwicklung/Bazaar/plugins\explorer\lib\wt_browser.py", line 628, in __init__
  File "C:/Program Files/Entwicklung/Bazaar/plugins\qbzr\lib\treewidget.py", line 1357, in __init__
  File "C:/Program Files/Entwicklung/Bazaar/plugins\qbzr\lib\treewidget.py", line 1693, in create_context_menu
  File "bzrlib\lazy_import.pyo", line 116, in __call__
  File "bzrlib\lazy_import.pyo", line 85, in _resolve
  File "bzrlib\lazy_import.pyo", line 200, in _import
  File "C:/Program Files/Entwicklung/Bazaar/plugins\qbzr\lib\diff.py", line 42, in <module>
  File "C:/Program Files/Entwicklung/Bazaar/plugins\qbzr\lib\util.py", line 128, in get_option
  File "C:/Program Files/Entwicklung/Bazaar/plugins\qbzr\lib\util.py", line 109, in _load
  File "bzrlib\util\configobj\configobj.pyo", line 1223, in __init__
  File "bzrlib\util\configobj\configobj.pyo", line 1306, in _load
ParseError: Invalid line at line "1".

0.656 couldn't find apport bug-reporting library: No module named apport
0.671 return code 4

-------------------------
When I run it from the Windows command shell, it gives the same message, but adds at the end

bzr 2.5.1 on python 2.6.6 (Windows-7-6.1.7600)
arguments: ['bzr', 'explore']
plugins: bzrtools[2.5.0], changelog_merge[2.5.1], colo[0.4.0],
    explorer[1.2.2], fastimport[0.14.0dev], git[0.6.8], launchpad[2.5.1],
    loom[2.3.0dev], netrc_credential_store[2.5.1], news_merge[2.5.1],
    pipeline[1.4.0], qbzr[0.22.3], rewrite[0.6.4dev], svn[1.2.2],
    upload[1.2.0dev], xmloutput[0.8.8]
encoding: 'cp1252', fsenc: 'mbcs', lang: None

*** Bazaar has encountered an internal error. This probably indicates a
    bug in Bazaar. You can help us fix it by filing a bug report at
        https://bugs.launchpad.net/bzr/+filebug
    including this traceback and a description of the problem.

Maybe this information is helpful.