When Migrating to .NET 4, Windows asks for user to enable .NET 3.51

I'm converting a fairly large project from using .NET 3.5 to .NET 4 using Visual Studio 2010. I made sure the Target Framework setting on each project file was set t开发者_JS百科o target .NET 4. I also converted third party dlls to .NET 4 or removed the dependancies. However, when I run my program on Windows 8 dev preview, it always pops up dialogs that asks user to enable .NET 3.51. I found that if I use an *.exe.config file it will suppress the dialog.

How do I check if I missed any assemblies that are still using .NET 3.5 or older references? Or is this caused by some other problem? Does *.exe manifest files affect .NET runtime version?

Please help if you have any idea what is wrong or you ran into something similar. Thanks in advance.

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Root cause is most likely one of the following in Windows 8 Preview:

1. Throws out "need to install 3.5.1" when it means "4.0"
2. Uses some 3.5.1 assemblies for UI bits regardless of what you have programmed in
3. Windows 8 defaults to 3.5.1 (missing config == reason to fail?) - most likely something hard coded in the OS temporarily

As far as your description, I would guess #3. As long as you are playing with a non-RTMed OS, I would bet there are some issues that people here will not be able to track down.