Visual Studio 2010: Properties.Settings broken after retargetting project to .NET Framework 3.5

Question

i've changed a project to target

• .NET Framework 3.5

rather than

• .NET Framework 4.

The project now crashes whenever i try to access settings:

Settings.Designer.cs:

      return ((global::System.Drawing.Font)(this["DefaultFont"]));

With the exception on `global::System.Drawing.Font)(this["DefaultFont"]));

An error occurred creating the configuration section handler for applicationSettings/GrobManagementSystem.Properties.Settings: Could not load file or assembly 'System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' or one of its dependencies. The system cannot find the file specified. (C:\Develop\Contoso\GrobFrobberemphasized text\GrobManagementSystem\GrobManagementSystem\bin\Debug\GrobManagementSystem.vshost.exe.config line 8)

The problem is that the MyApp.exe.config contains references to .NET Framework 4.0 (4.0.0.0):

<?xml version="1.0"?>
<configuration>
    <configSections>
        <sectionGroup name="userSettings" 
              type="System.Configuration.UserSettingsGroup, System, 
                    Version=4.0.0.0, 
                    Culture=neutral, PublicKeyToken=b77a5c561934e089">

This file is generated on every build, and it based on the contents of Settings.settings (an xml file that doesn't mention 4.0.0.0 anywhere):

<?xml version='1.0' encoding='utf-8'?>
<SettingsFile xmlns="http://schemas.microsoft.com/VisualStudio/2004/01/settings" CurrentProfile="(Default)" GeneratedClassNamespace="GrobManagementSystem.Properties" GeneratedClassName="Settings">
  <Profiles />
  <Settings>

There's also the settings code-behind file (Settings.Designer.cs), that also doesn't mention 4.0.0.0 anywhere:

namespace GrobManagementSystem.Properties {


    [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
    [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.VisualStudio.Editors.SettingsDesigner.SettingsSingleFileGenerator", "10.0.0.0")]
    internal sealed partial class Settings : global::System.Configuration.ApplicationSettingsBase {

        private static Settings defaultInstance = ((Settings)(global::System.Configuration.ApplicationSettingsBase.Synchronized(new Settings())));

        public static Settings Default {
            get {
                return defaultInstance;
            }
        }

Why is the generated MyApp.exe.config referencing .NET 4.0 (i.e. 4.0.0.0), when the project isn't 4.0:

and the designers aren't 4.0?

And the larger question:

How do i retarget a project to .NET Framework 3.5 from .NET Framework 4.0?

Guaranty

Answer 1

Found the answer, delete app.config.

app.config is automatically created based on settings.settings. Visual Studio was not building it, even though it needed to be updated.

Note: Clean and rebuild doesn't force visual studio to clean and rebuild it

Deleting it, to force Visual Studio to rebuild, it fixed it.

Guaranty

Don't delete it if you have app.config settings of your own in there! (outside of the .settings file, that is..) --The linked answer goes on to explain however, that when you revert back from 4.0, that it does not pull out all the 4.0 constructs, so 3.5 freaks out. in my case, I just did a diff to a previously working commit and could see what it inserted when I went to 4.0 – Moussorgsky