.net framework compatibility questions

Question

I am newbie to the .NET Framework. I have some a question about .NET program execution.

If I am developing a .NET application using .NET Framework version 4.0, can that

Answer 1

No, you cannot reference a DLL compiled in .NET 4.0 from a program compiled in .NET 3.5. .NET Framework applications are usually backward compatible -- that is, you can reference a .NET 3.5 assembly from .NET 4.0 code, but the reverse is not true.

You could try compiling the .NET 3.5 project in 4.0, or compiling the .NET 4.0 assembly in .NET 3.5, either of which will work if they are an option.