title: SharpSSH invalid privatekey
body: <p>I use SharpSSH to connect to a stfp-server.</p>
  
  <p>This for I need to add a privatekey-file like this:</p>
  
  <pre><code>sftp.AddIdentityFile(KeyFilePath);
  </code></pre>
  
  <p>But this throws an exception:</p>
  
  <pre><code>invaid privatekey: C:\KeyFile\privatekey_2.ppk
  </code></pre>
  
  <p>The file was created with puttygen and works with filezilla.
  The privatekey-type doesn't matter (SSH-1 RSA, SSH-2 RSA, SSH-2 DSA). Everytime the same result.</p>
  
  <p>Do you know how to handle this problem?</p>