Backwards Compatibility of .NET Framework 4

Question

We have an WPF Application build on .net framework 3.5.

Some testers find if they uninstall .net framework 3.5, but install .net framework 4.0, our APP fails to laun

Answer 1

.Net 3.5/2.0 Applications do not automatically run on the .Net 4.0 runtime. You have to specify explicitly for your application that it should run on .Net 4.0 in your App.config by adding:

In case you have third party components you also have to mark them as being ready for 4.0:

   ...
   
      ...
      
         ...
         
            
            
         
         ...
      
      ...
   
   ...