updated and will not show designers

The errors indicate that Windows Forms Designer cannot load the base types it needs to design your forms.

For the message:

The designer could not be shown for this file because none of the classes within it can be designed.

This occurs when Visual Studio cannot find or load a base class that satisfies designer requirements. Typical causes include:

1. The base form/control is in an assembly that cannot be loaded by the designer (for example, compiled only for x64/Itanium).
2. The class does not inherit from a designer-supported base type.
3. The project has not been built after changes.

Actions:

1. Build the entire solution so all referenced assemblies are compiled.
2. Ensure each form/control class derives from a designer-supported base class (for example, System.Windows.Forms.Form or UserControl).
3. If any base forms are defined in a separate project/assembly, make sure that project is referenced and successfully built.
4. If the base form(s) are in an assembly compiled as x64 or Itanium, change that project’s Platform Target/CPU to AnyCPU, rebuild, and then reopen the designer. Visual Studio is a 32-bit process and cannot execute code from a 64-bit-only module in the designer.

For the message:

The type System.Configuration.ApplicationScopedSettingAttribute could not be found.

This means the designer cannot resolve that type at design time. This is treated like any other “type could not be found” error and will block the designer.

Actions:

1. Build the project and check the Error List for any compile errors related to missing references or namespaces.
2. Ensure the project references the correct .NET assemblies and that the code using ApplicationScopedSettingAttribute has the proper using/Imports and target framework.
3. Fix any code errors in the form’s code-behind (including InitializeComponent) that prevent the designer from loading.

Once the underlying type and reference issues are resolved and the solution builds cleanly, reopen the form in Design view; the designer should load instead of the error page.

References:

• Windows Forms Designer error page
• Cannot Display Inherited Form in Form Designer When Base Form Defined in 64-bit Assembly

Hello @Jay O'Brien ,

Thanks for your question.

The error The type 'System.Configuration.ApplicationScopedSettingAttribute' could not be found means Visual Studio can't resolve types from System.Configuration.

You can refer to following steps:

1. Check the Error List for compile errors across the whole project. The designer won't load any form if the project fails to build. Fix all compile errors first before proceeding.
2. Add the Missing NuGet Package.

In your .csproj (use the latest stable version, for ex: 8.0.0):

<PackageReference Include="System.Configuration.ConfigurationManager" Version="8.0.0" />

3. In your .csproj, confirm you're targeting the right framework:

<!-- For .NET Framework-->
<TargetFramework>net48</TargetFramework>

<!-- For modern .NET with WinForms -->
<TargetFramework>net8.0-windows</TargetFramework>

4. Sometimes a stale build causes the designer to fail:

• Build -> Clean solution
• Build -> Rebuid solution
• Delete the bin/ and obj/ folders manually, then rebuild.

5. If the update itself broke something, please repair visual studio.

• Open Visual Studio Installer.
• Click More → Repair on your installed version.

I hope this addresses your question. If this response was helpful, please consider following the guidance to provide feedback.