Impossible to login when some calendars have been created

Here is the error message:

UnboundLocalError
Sorry, a site error occurred.

Traceback (innermost last):

    * Module ZPublisher.Publish, line 196, in publish_module_standard
    * Module Products.Localizer, line 58, in new_publish
    * Module ZPublisher.Publish, line 146, in publish
    * Module Zope2.App.startup, line 222, in zpublisher_exception_hook
    * Module ZPublisher.Publish, line 115, in publish
    * Module ZPublisher.mapply, line 88, in mapply
    * Module ZPublisher.Publish, line 41, in call_object
    * Module Shared.DC.Scripts.Bindings, line 311, in __call__
    * Module Shared.DC.Scripts.Bindings, line 348, in _bindAndExec
    * Module Products.CMFCore.FSPageTemplate, line 195, in _exec
    * Module Products.CMFCore.FSPageTemplate, line 134, in pt_render
    * Module Products.PageTemplates.PageTemplate, line 104, in pt_render
      <FSPageTemplate at /cps/login_form>
    * Module TAL.TALInterpreter, line 238, in __call__
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 457, in do_optTag_tal
    * Module TAL.TALInterpreter, line 442, in do_optTag
    * Module TAL.TALInterpreter, line 437, in no_tag
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 749, in do_useMacro
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 457, in do_optTag_tal
    * Module TAL.TALInterpreter, line 442, in do_optTag
    * Module TAL.TALInterpreter, line 437, in no_tag
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 715, in do_condition
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 749, in do_useMacro
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 715, in do_condition
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 457, in do_optTag_tal
    * Module TAL.TALInterpreter, line 442, in do_optTag
    * Module TAL.TALInterpreter, line 437, in no_tag
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 691, in do_loop_tal
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 457, in do_optTag_tal
    * Module TAL.TALInterpreter, line 442, in do_optTag
    * Module TAL.TALInterpreter, line 437, in no_tag
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 691, in do_loop_tal
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 457, in do_optTag_tal
    * Module TAL.TALInterpreter, line 442, in do_optTag
    * Module TAL.TALInterpreter, line 437, in no_tag
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 715, in do_condition
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 457, in do_optTag_tal
    * Module TAL.TALInterpreter, line 442, in do_optTag
    * Module TAL.TALInterpreter, line 437, in no_tag
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 691, in do_loop_tal
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 457, in do_optTag_tal
    * Module TAL.TALInterpreter, line 442, in do_optTag
    * Module TAL.TALInterpreter, line 437, in no_tag
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 715, in do_condition
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 455, in do_optTag_tal
    * Module TAL.TALInterpreter, line 437, in no_tag
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 715, in do_condition
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 457, in do_optTag_tal
    * Module TAL.TALInterpreter, line 442, in do_optTag
    * Module TAL.TALInterpreter, line 437, in no_tag
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 715, in do_condition
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 457, in do_optTag_tal
    * Module TAL.TALInterpreter, line 442, in do_optTag
    * Module TAL.TALInterpreter, line 437, in no_tag
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 457, in do_optTag_tal
    * Module TAL.TALInterpreter, line 442, in do_optTag
    * Module TAL.TALInterpreter, line 437, in no_tag
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 749, in do_useMacro
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 457, in do_optTag_tal
    * Module TAL.TALInterpreter, line 442, in do_optTag
    * Module TAL.TALInterpreter, line 437, in no_tag
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 715, in do_condition
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 457, in do_optTag_tal
    * Module TAL.TALInterpreter, line 442, in do_optTag
    * Module TAL.TALInterpreter, line 437, in no_tag
    * Module TAL.TALInterpreter, line 281, in interpret
    * Module TAL.TALInterpreter, line 507, in do_setLocal_tal
    * Module Products.PageTemplates.TALES, line 221, in evaluate
      URL: file:CPSSkins/skins/cpsskins_cps3/cpsskins_lib.pt
      Line 5, Column 4
      Expression: <PythonExpr content.render_cache(shield=shield, context_obj=here, enable_esi=enable_esi, boxedit=boxedit, template=template)>
      Names:

      {'container': <CPSDefaultSite at /cps>,
       'context': <CPSDefaultSite at /cps>,
       'default': <Products.PageTemplates.TALES.Default instance at 0x4104a1ac>,
       'here': <CPSDefaultSite at /cps>,
       'loop': <Products.PageTemplates.TALES.SafeMapping object at 0x438c88cc>,
       'modules': <Products.PageTemplates.ZRPythonExpr._SecureModuleImporter instance at 0x4106ec6c>,
       'nothing': None,
       'options': {'args': ()},
       'repeat': <Products.PageTemplates.TALES.SafeMapping object at 0x438c88cc>,
       'request': <HTTPRequest, URL=http://localhost:8080/cps/login_form>,
       'root': <Application at >,
       'template': <FSPageTemplate at /cps/login_form>,
       'traverse_subpath': [],
       'user': <SpecialUser 'Anonymous User'>}

    * Module Products.PageTemplates.ZRPythonExpr, line 47, in __call__
      __traceback_info__: content.render_cache(shield=shield, context_obj=here, enable_esi=enable_esi, boxedit=boxedit, template=template)
    * Module Python expression "content.render_cache(shield=shield, context_obj=here, enable_esi=enable_esi, boxedit=boxedit, template=template)", line 1, in <expression>
    * Module Products.CPSSkins.PortalBoxGroup, line 342, in render_cache
    * Module Products.CPSSkins.PortalBoxGroup, line 286, in render
    * Module Products.CPSPortlets.CPSPortlet, line 504, in render_cache
    * Module Products.CPSDocument.CPSDocument, line 70, in render
    * Module Products.CPSDocument.FlexibleTypeInformation, line 753, in renderObject
    * Module Products.CPSDocument.FlexibleTypeInformation, line 715, in _renderLayouts
    * Module Products.CPSSchemas.Layout, line 400, in renderLayoutStructure
    * Module Products.CPSPortlets.CPSPortletWidget, line 78, in render
    * Module Products.CMFCore.FSPythonScript, line 108, in __call__
    * Module Shared.DC.Scripts.Bindings, line 311, in __call__
    * Module Shared.DC.Scripts.Bindings, line 348, in _bindAndExec
    * Module Products.CMFCore.FSPythonScript, line 164, in _exec
    * Module None, line 162, in sharedcalendar_portlet_view
      <FSPythonScript at /cps/sharedcalendar_portlet_view used for /cps/portal_layouts/sharedcalendar_portlet/w__portal>
      Line 162

UnboundLocalError: local variable 'calendar' referenced before assignment (Also, the following error occurred while attempting to render the standard error message, please see the event log for full details: local variable 'calendar' referenced before assignment)

Fixed with changeset [52567].