title: sp_send_dbmail does not attach the file to the email
body: <p>I have the following code:   </p>
  
  <pre><code>DECLARE
  
  @ATTACH_FILE nvarchar (max),
  @SQL varchar (max);
  
  /* ============================================================== */  
  
  -- add files to attach
      SET @ATTACH_FILE = N'\\C:\attach\file.txt';
  
  SET @SQL = 'exec msdb.dbo.sp_send_dbmail
  @profile_name = ''ProfileMail'',
  @recipients = ''my@mail.ru'',
  @reply_to = ''my@mail.ru'',
  @subject = ''subject mail'',
  @body = ''body mail'',
  @file_attachments='' '+ @ATTACH_FILE +' '' ';
  
  -- send mail
      EXEC(@SQL);
  </code></pre>
  
  <p><strong>UPD</strong> remove the two slashes SET @ATTACH_FILE = N'C:\attach\file.txt'; - the error persists  </p>
  
  <p>I receive an error: Invalid file attachment \C:\attach\file.txt (file is located on a sql server).<br>
  I do not understand what the problem is.   </p>