c# app doesn't work on XP

Question

i made a app that uses the watIn library , and target to .NET 3.5 (so it will work on XP to). after i published the app on my PC, i installed it, and it worked well. but, when i tried it on different PC running XP, it didn't work. i made sure the PC I'm testing on is running .NET 3.5 or grater.

I'm running windows 7 and visual studio 2010.

the program work on Windows 7 (tried that on 2 PC's). the program doesn't work on XP (tried that on 2 PC's).

On Xp i get this message:

Unable to install or run the application. The application requires that
assembly WindowsBase Version 3.0.0.0 be installed in the Global
Assembly Cache (GAC) first.

Please contact your administrator 

my questions:

1. what should i do to make sure it work on XP?

2. if i start the development on .net 4, and then switch it to 3.5 and it still run, that mean i only used 3.5 code/features from the get go?

3. will visual studio give me compile Error if i run 4.0 code on app that i change his properties to target .net 3.5 in the middle of development?

4. is there a way to install the .net 3.5 framework with my app installer? (if it doesn't already got 1 on the PC)

(sorry for my English)

Answer 1

Make sure that the PC's running XP have .NET installed on them. Windows 7 will already come with the .NET Framework installed, but XP doesn't have the newer versions of the framework.

Also, if your project requires a specific version of the .NET framework, it's good to add it as a prerequisite in your setup installer.

Also, in your build, make sure you're targeting the proper framework.

links:
- http://www.microsoft.com/net/download
- http://www.codeproject.com/Articles/35976/Add-Prerequisites-of-NET-Framework-in-Visual-Studi