Hello,
Usually .net application needs specified .net framework to run. You could refer to this
article to veirfy that whether your OS has included some .net framework as OS component.
In addition, have you got any .net framework installed on your machine? When you mention 'changed the compile options from using .NET 2.0 to 3.5', do you mean change the target framework of the project from 2.0 to 3.5? If so, now that you do not take advantage of .net framework 3.5's new functionality, as I understand, the application could work with .net framework 2.0 installed.
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