title: C#: An exception has been encountered. This may be caused by an extension
body: <p>I'm running with VS-2013 Ultimate. While executing my code, I'm getting this error message box:</p>
  
  <pre><code>An exception has been encountered. This may be caused by an extension
  </code></pre>
  
  <p>When entering the log file (the path is mentioned on the message), I'm get this exception:</p>
  
  <pre><code>  &lt;entry&gt;
      &lt;record&gt;905&lt;/record&gt;
      &lt;time&gt;2014/08/22 15:46:25.494&lt;/time&gt;
      &lt;type&gt;Error&lt;/type&gt;
      &lt;source&gt;Editor or Editor Extension&lt;/source&gt;
      &lt;description&gt;
          System.NullReferenceException: Object reference not set to an instance of an object.&amp;#x000D;&amp;#x000A;
              at Microsoft.VisualStudio.Debugger.Parallel.UI.ThreadMarkerGenerator.LocationMatchesTagger(DocumentContext location, MarkerTagger tagger)&amp;#x000D;&amp;#x000A;
              at Microsoft.VisualStudio.Debugger.Parallel.UI.ThreadMarkerGenerator.&amp;lt;&amp;gt;c__DisplayClass1.&amp;lt;GetMarkersForTagger&amp;gt;b__0(ThreadMarker marker)&amp;#x000D;&amp;#x000A;
              at System.Linq.Enumerable.WhereListIterator`1.MoveNext()&amp;#x000D;&amp;#x000A;
              at Microsoft.VisualStudio.Debugger.Parallel.Extension.MarkerTagger.&amp;lt;GenerateTagList&amp;gt;d__a.MoveNext()&amp;#x000D;&amp;#x000A;
              at System.Linq.Buffer`1..ctor(IEnumerable`1 source)&amp;#x000D;&amp;#x000A;
              at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)&amp;#x000D;&amp;#x000A;
              at Microsoft.VisualStudio.Debugger.Parallel.Extension.MarkerTagger..ctor(ITextBuffer buffer, ITextDocument document)&amp;#x000D;&amp;#x000A;
              at Microsoft.VisualStudio.Debugger.Parallel.Extension.MarkerTaggerProvider.CreateTagger[T](ITextBuffer buffer)&amp;#x000D;&amp;#x000A;
              at Microsoft.VisualStudio.Text.Tagging.Implementation.TagAggregator`1.GatherTaggers(ITextBuffer textBuffer)
          &lt;/description&gt;
    &lt;/entry&gt;
  </code></pre>
  
  <p>I'm sure that this code already worked well in the past.
  What could be the reason?</p>