title: The "TransformXml" task failed unexpectedly
body: <p>Our project was updated to use .net 4.5.1 from .net 4.0. After downloading and updating the .net 4.5.1 in my VS 2012,i am ending up with error below. can any one help to solve the issue</p>
  
  <pre><code>The "TransformXml" task failed unexpectedly.
  System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.Web.XmlTransform, Version=1.4.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.
  File name: 'Microsoft.Web.XmlTransform, Version=1.4.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'
     at Microsoft.Web.Publishing.Tasks.TransformXml.Execute()
     at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute()
     at Microsoft.Build.BackEnd.TaskBuilder.&lt;ExecuteInstantiatedTask&gt;d__20.MoveNext()
  </code></pre>