Rebex File Transfer Pack supports all version of .NET framework which are supported by Microsoft.
Microsoft main support phase for .NET Framework 1.1 ended on 2008-10-14. They will still be releasing security fixes for .NET 1.1 till 2013-10-08.
It's the same with Rebex File Transfer Pack. We stopped releasing .NET 1.1. versions of Rebex File Transfer Pack after Microsoft stopped supporting it. We will provide security fixes till 2013-10-08. For details see the Knowledge Base article Rebex support lifecycle for various .NET framework versions.
Please note that Rebex customers are still able to download all versions released before the end of their support contact. They are even able to download all versions released before their purchase date. When you order Rebex File Transfer Pack today, you'll be able to download .NET 1.1. binaries for build 3793 (released at 2010-03-11).
Please note that these outdated releases are unsupported. It might be impossible to fully support component for specific .NET Framework when this specific framework is no longer supported by Microsoft. We might still be able to help .NET 1.1 users who run into problems, but we can't guarantee anything.