The answer might be interesting to others in the similar situation so I post it here as well:

Both SFTP and FTP references the Rebex.Net.ProxySocket.dll. .NET does not allow using two different versions of the same assembly within the same application. If you have to use both SFTP and FTP in the same app you have to use the both assemblies with the same build number (because they reference the same Rebex.Net.ProxySocket.dll).

Let's consider following example. User has a valid license for following components:

• Rebex.Net.Ftp.dll version 2.5.3127.0 (build number 3227, active support contract)
• Rebex.Net.Sftp.dll version 1.5.2800.0 (build number 2800, expired support contract)

There are following options:

• Downgrade to the newest build supported by both components. All users with a valid license can download all older versions of the licensed component (just login to Members area and navigate to Download archive). This would be free of charge, but you'll lose all new features and bugfixes released between builds 2800 and 3227.

• Renew the support contract for the older component so you will be able to download the most current version. It will give you the most current version but has one drawback. Your support contract for SFTP and FTP will have different end dates. It might again result in situation in which you'll be able to download the latest version for only one of the components.

• Upgrade to the Rebex File Transfer Pack (pack of FTP and SFTP with discounted price) or Rebex Total Pack (all Rebex components in one pack). This will ensure that you always have compatible versions of the components available. Contact us at support@rebex.net for upgrade pricing or log on to your account at www.rebex.net/protected to upgrade directly.