What Version of .Net framework should I install?

I wrote a VB.net dll that is referenced by an Access 2003 application, and the application needs to run on Windows XP computers.  I'm currently in the process of deploying a Windows Server 2008 R2 Server that will service about 20 thin clients.  What version of .net framework should I select as the target framework for the VB.net dll, what version should I install on the Windows XP clients, and what version should I install on the Windows Server 2008 R2 server?  Is version 4.0 that latest version that will run on Windows XP?  Will the application run on the Windows Server 2008 R2 Server if the Server has 4.6 but the .dll is targeted for version 4.0 (i.e. Are all the versions backwards compatible)?  Also, why does version 4.5.2 seem to be more popular than 4.6 (the VB app defaulted to this version even though it's not the latest, and it seems to be the most downloaded version)?
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Éric MoreauSenior .Net ConsultantCommented:
4.6 is only available since July 2015 when VS2015 was released.

.Net Framework 4.0 is the last one to run on XP but I think you need SP3.

If it runs on 4.0, it will also runs on Windows Server 2008 r2. And yes the application targeting 4.0 will run on the server if 4.6 is installed.
JohnBusiness Consultant (Owner)Commented:
For Windows 10 (and I need to check Server 2012) .NET 4.6 installs automatically. I have it running and it appears to be fine. I got the newest version of .NETFX Setup Verifier and 4.6 verifies fine.

For Window 7 (and likely Server 2008) you need to go to Microsoft, search for .NET 4.6, download it and install it.
Jacques Bourgeois (James Burger)PresidentCommented:
Éric is right in his affirmations and assumptions. 4.6 is downloaded less often because it is newer, you need 4.0 SP3 for Windows XP, and all the 4.x versions are backward compatibles with older 4.x versions.

One thing that is important however, because you will be working with Access 2003, thus .mdb files, is to set the target CPU to x86. If you target the usually recommended Any CPU or try to force x64, you will get an error message telling you that the JET database engine (the real thing behind Access) is not installed on the computer, even if it is.

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Declan_BasileITAuthor Commented:
Thank you.
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