Framework supported by your application
Since Microsoft published the Framework 4.0, your old applications (using .NET 2.0, 3.5 or 3.5 SP1) can not run… because, if the user has only installed the Framework 4, your application try to find a folder C:\Windows\Microsoft.NET\v3.5. And this folder does not exist !
If you add the supportedRuntime tag in your app.config file, you allow that your application 2.0 or 3.5 can run with the Framework 4.
<?xml version="1.0" encoding="utf-8"?> <configuration> <startup> <supportedRuntime version="v4.0.30319"/> <supportedRuntime version="v2.0.50727"/> </startup> </configuration>