title: Receiving Invalid Signature - SFTP
body: <p>Our file transfer automation software is connecting to an external SFTP server to download files. It's connecting using Putty's command line tool PSFTP. When it kicks off at it's scheduled time, an error results. The error is:</p>
  <pre><code>Remote working directory is /directory
  lcd: unable to change directory: Invalid Signature.
  
  Using username &quot;username&quot;.
  Pre-authentication banner message from server:
  | IM CCaaS  FTP server
  End of banner message from server
  </code></pre>
  <p>When I manually FTP to the server, I can log in with no issue. I then re-run the job and it completes successfully. I've googled this and found articles on key exchanges with similar errors, but this connection isn't using private/public keys. I cut over the application to a new Windows 2016 server on September 21st. There have been some successful transfers. I've also read the version of PSFTP may be the issue (0.73), but I would have expected consistent issues connecting. It seems sporadic. I'm not sure if the issue is on my end or at the destination. Any thoughts?</p>