title: How to determine cause of VS2013 error in editor extension
body: <p>When I attach the debugger to a web page, as soon as a the first breakpoint is hit I get an error dialog saying "An exception has been encountered. This may be caused by an extension.".</p>
  
  <p>In ActivityLog.xml I find this:</p>
  
  <pre><code>type: Error
  source: Editor or Editor Extension
  description: 
  System.ArgumentNullException: Value cannot be null.&amp;#x000D;&amp;#x000A;Parameter name: sp&amp;#x000D;&amp;#x000A;
  at Microsoft.VisualStudio.Shell.ServiceProvider..ctor(IServiceProvider sp, Boolean defaultServices)&amp;#x000D;&amp;#x000A;
  at Microsoft.VisualStudio.Web.HTML.Implementation.ContainedLanguage.ContainedLanguageHostAdapter.Microsoft.Web.Editor.ContainedLanguage.IContainedLanguageHost.get_BufferGraph()&amp;#x000D;&amp;#x000A;
  at Microsoft.CSS.Editor.SyntaxCheck.CssErrorTag..ctor(ITextBuffer textBuffer, ICssError error)&amp;#x000D;&amp;#x000A;
  at Microsoft.CSS.Editor.SyntaxCheck.CssErrorTagger.CollectTags(SnapshotSpan span, CssErrorList errors, SortedRangeList`1 tagSpans)&amp;#x000D;&amp;#x000A;
  at Microsoft.CSS.Editor.SyntaxCheck.CssErrorTagger.GetTags(NormalizedSnapshotSpanCollection spans)&amp;#x000D;&amp;#x000A;
  at Microsoft.VisualStudio.Text.Tagging.Implementation.TagAggregator`1.&amp;lt;GetTagsForBuffer&amp;gt;d__5.MoveNext()
  </code></pre>
  
  <p>None of which points to anything I am familiar with.</p>