KeyError during restrictedTraverse

You have a traceback similiar to this:

Traceback (innermost last):
  Module ZPublisher.Publish, line 113, in publish
  Module ZPublisher.mapply, line 88, in mapply
  Module ZPublisher.Publish, line 40, in call_object
  Module Products.Archetypes.BaseFolder, line 57, in __call__
  Module Shared.DC.Scripts.Bindings, line 311, in __call__
  Module Shared.DC.Scripts.Bindings, line 348, in _bindAndExec
  Module Products.CMFCore.FSPageTemplate, line 188, in _exec
  Module Products.CMFCore.FSPageTemplate, line 127, in pt_render
  Module Products.PageTemplates.PageTemplate, line 102, in pt_render
   - <FSPageTemplate at /Plone/base_view used for /Plone/usability>
  Module TAL.TALInterpreter, line 206, in __call__
  Module TAL.TALInterpreter, line 250, in interpret
  Module TAL.TALInterpreter, line 709, in do_useMacro
  Module TAL.TALInterpreter, line 250, in interpret
  Module TAL.TALInterpreter, line 426, in do_optTag_tal
  Module TAL.TALInterpreter, line 411, in do_optTag
  Module TAL.TALInterpreter, line 406, in no_tag
  Module TAL.TALInterpreter, line 250, in interpret
  Module TAL.TALInterpreter, line 740, in do_defineSlot
  Module TAL.TALInterpreter, line 250, in interpret
  Module TAL.TALInterpreter, line 426, in do_optTag_tal
  Module TAL.TALInterpreter, line 411, in do_optTag
  Module TAL.TALInterpreter, line 406, in no_tag
  Module TAL.TALInterpreter, line 250, in interpret
  Module TAL.TALInterpreter, line 688, in do_defineMacro
  Module TAL.TALInterpreter, line 250, in interpret
  Module TAL.TALInterpreter, line 732, in do_defineSlot
  Module TAL.TALInterpreter, line 250, in interpret
  Module TAL.TALInterpreter, line 426, in do_optTag_tal
  Module TAL.TALInterpreter, line 411, in do_optTag
  Module TAL.TALInterpreter, line 406, in no_tag
  Module TAL.TALInterpreter, line 250, in interpret
  Module TAL.TALInterpreter, line 688, in do_defineMacro
  Module TAL.TALInterpreter, line 250, in interpret
  Module TAL.TALInterpreter, line 426, in do_optTag_tal
  Module TAL.TALInterpreter, line 411, in do_optTag
  Module TAL.TALInterpreter, line 406, in no_tag
  Module TAL.TALInterpreter, line 250, in interpret
  Module TAL.TALInterpreter, line 709, in do_useMacro
  Module TAL.TALInterpreter, line 250, in interpret
  Module TAL.TALInterpreter, line 477, in do_setLocal_tal
  Module Products.PageTemplates.TALES, line 221, in evaluate
   - URL: file:Archetypes/skins/archetypes/base.pt
   - Line 82, Column 8
   - Expression: standard:'field_macro | here/widgets/field/macros/view'
   - Names:
      {'container': <PloneSite at /Plone>,
       'context': <ApplicationFolder at /Plone/usability>,
       'default': <Products.PageTemplates.TALES.Default instance at 0x0145B670>,
       'here': <ApplicationFolder at /Plone/usability>,
       'loop': <Products.PageTemplates.TALES.SafeMapping object at 0x0450F120>,
       'modules': <Products.PageTemplates.ZRPythonExpr._SecureModuleImporter instance at 0x0144E800>,
       'nothing': None,
       'options': {'args': ()},
       'repeat': <Products.PageTemplates.TALES.SafeMapping object at 0x0450F120>,
       'request': <HTTPRequest, URL=http://localhost/usability>,
       'root': <Application at >,
       'template': <FSPageTemplate at /Plone/base_view used for /Plone/usability>,
       'traverse_subpath': [],
       'user': admin}
  Module Products.PageTemplates.Expressions, line 183, in __call__
  Module Products.PageTemplates.Expressions, line 171, in _eval
  Module Products.PageTemplates.Expressions, line 127, in _eval
   - __traceback_info__: here
  Module Products.PageTemplates.Expressions, line 306, in restrictedTraverse
   - __traceback_info__: {'path': ['widgets', 'field', 'macros', 'view'], 'TraversalRequestNameStack': ['view', 'macros']}
  Module OFS.ObjectManager, line 704, in __getitem__
KeyError: 'field'

Looks like something was unable to access "field" which is part of some object. Crucial information here is traceback_info:

__traceback_info__: {'path': ['widgets', 'field', 'macros', 'view'], 'TraversalRequestNameStack': ['view', 'macros']}

Here you can see page template path which was accessed. In this case, it was widgets/field.pt -> macros/view. Page template was unable to find field.pt in widgets directory, thus KeyError: "field".

This is caused by missing files in skin folders. In my case, I had created widgets folder under the skin folder of my own product. This override Archetypes internal skin folder, thus making field.pt unavailable. The solution was to rename my skins/usability/widgets folder to skins/usability/usability_widgets.