I have done something and can no longer edit the manage display pages for the article content type . When I try to visit them I fall out of the usual rich html interface into a page whose code is attached below. I think that this is happening because I have accidentally damaged or removed the full content view mode for the article, but I am a newbie so I am really not sure. I was playing with Display Suite when this problem began.
Any ideas what is going on? and how to fix it? Thanks.
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<h2 class="element-invisible">You are here</h2><div class="breadcrumb"><a href="/drupal7/">Home</a> » <a href="/drupal7/?q=admin">Administration</a> » <a href="/drupal7/?q=admin/structure" title="Administer blocks, content types, menus, etc.">Structure</a> » <a href="/drupal7/?q=admin/structure/types" title="Manage content types, including default status, front page promotion, comment settings, etc.">Content types</a> » <a href="/drupal7/?q=admin/structure/types/manage/article">Article</a></div> <h1 class="page-title">Article</h1>
<div class="add-or-remove-shortcuts add-shortcut"><a href="/drupal7/?q=admin/config/user-interface/shortcut/shortcut-set-1/add-link-inline&link=admin/structure/types/manage/article/display&name=Article&destination=admin/structure/types/manage/article/display&token=sfNEjW3fhzg0KSwbxJKEEx_mwmWcqqCQjgxWGn5Q27A"><span class="icon"></span><span class="text">Add to <em class="placeholder">Default</em> shortcuts</span></a></div> <h2 class="element-invisible">Primary tabs</h2><ul class="tabs primary"><li><a href="/drupal7/?q=admin/structure/types/manage/article">Edit</a></li>
<li><a href="/drupal7/?q=admin/structure/types/manage/article/fields">Manage fields</a></li>
<li class="active"><a href="/drupal7/?q=admin/structure/types/manage/article/display" class="active">Manage display<span class="element-invisible">(active tab)</span></a></li>
<li><a href="/drupal7/?q=admin/structure/types/manage/article/comment/fields">Comment fields</a></li>
<li><a href="/drupal7/?q=admin/structure/types/manage/article/comment/display">Comment display</a></li>
</ul> </div>
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<div class="tabs-secondary clearfix"><ul class="tabs secondary"><h2 class="element-invisible">Secondary tabs</h2><ul class="tabs secondary"><li class="active"><a href="/drupal7/?q=admin/structure/types/manage/article/display" class="active">Default<span class="element-invisible">(active tab)</span></a></li>
<li><a href="/drupal7/?q=admin/structure/types/manage/article/display/teaser">Teaser</a></li>
</ul></ul></div>
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<p>Content items can be displayed using different view modes: Teaser, Full content, Print, RSS, etc. <em>Teaser</em> is a short format that is typically used in lists of multiple content items. <em>Full content</em> is typically used when the content is displayed on its own page.</p><p>Here, you can define which fields are shown and hidden when <em class="placeholder">Article</em> content is displayed in each view mode, and define how the fields are displayed in each view mode.</p>
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