title: The designer could not be shown for this file because none of the classes within it can be designed
body: <p>Yes I already searched and the solution on this <a href="https://stackoverflow.com/questions/6683255/the-designer-could-not-be-shown-for-this-file-because-none-of-the-classes-within">post</a> didnt work, my scenario is different.</p>
  
  <p>I have a winform application, very simple, it was working, and now the error on the title of this post is shown when I try to open the form.<br>
  The only thing I have done is installed VS11 developer preview and vs 2010 SP1.</p>
  
  <p>Any idea how to fix this?></p>