title: C# error: adding reference to .dll file
body: <p>I have my project file and Calculator01.dll file in same directory. When I'm trying to add a reference to Calculator.dll file message box appears and show </p>
  
  <blockquote>
    <p>"A reference to 'E\IT131344............Calculato01.dll could not be added. Please make sure file is accessible and that it is a valid assembly or COM component."</p>
  </blockquote>
  
  <p>I have already marked class functions with in <code>CalDllWrapper</code> class;</p>
  
  <pre><code>[DllImport("Calculator01.dll")]
  </code></pre>
  
  <p>Solutions I have found so far does not work for me. What can I do to resolve this problem? Please help me.
  thanks in advance</p>