title: Visual studio 2017 not treating csproj as a valid project file after conversion from netstandard to framework
body: <p>The following was done in VS Enterprise 2017 15.8.2.  I had converted a .NET Framework project (C#) into netstandard and then had to convert it back due to a build issue.  The conversion was done by restoring a previous commit from git.  However, now VS does not recognize the project as a valid project.  The linked unit test project generates the warning</p>
  
  <blockquote>
    <p>the referenced component '&lt; project name >' could not be found.</p>
  </blockquote>
  
  <p>Attempts to view the project properties produces the error</p>
  
  <blockquote>
    <p>An error occurred trying to load the project properties window.  Close
    the window and try again. Member not found. (Exception from HRESULT:
    0x80020003 (DISP_E_MEMBERNOTFOUND))</p>
  </blockquote>
  
  <p>The build selection options disappear from the build menu and the build/debug options are gone from the project context menu.  The dependencies node of the solution explorer is empty.  I have seen other posts in which people describe a similar condition that is resolved by either reopenning the solution or changing the mode of vs to a different type of development or deleting bin/obj.  None of these worked, nor a full reboot.  Given that this project file used to be framework I suspect there is something cached somewhere that is covered by my .gitignore which needs to be deleted.</p>