Error on Form Designer on Visual Studio 2012

Question

Dear Sir,
I have used Visual Studio 2012 to develop my project for a long time.
However, suddenly Designer of all Forms come an error but the system can compile the project.
Therefore, I am not able to change the design of the Form in Visual Studio.
Any Suggestion?
Thank you very much.
The following is the Error of the Designer:
To prevent possible data loss before loading the designer, the following errors must be resolved:
1 Error
The type 'System.Configuration.UserScopedSettingAttribute' could not be found. Ensure that the assembly containing the type is referenced. If the assembly is part of the current development project, ensure that the project has been built.
Instances of this error (1)
1. Hide Call Stack
at Microsoft.VisualStudio.Design.VSTypeResolutionService.System.ComponentModel.Design.ITypeResolutionService.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase)
at Microsoft.VisualStudio.Design.VSTypeResolutionService.System.ComponentModel.Design.ITypeResolutionService.GetType(String name, Boolean throwOnError)
at Microsoft.VisualStudio.Shell.Design.VirtualTypeBuilder.FillAttributes(Resolver resolver, CodeTypeMember member, Attribute[]& customAttributes, MemberAttributes& memberAttributes)
at Microsoft.VisualStudio.Shell.Design.VirtualTypeBuilder.InitializeFromType(ITypeResolutionService typeResolutionService, CodeTypeDeclaration typeDecl, String namespaceName)
at Microsoft.VisualStudio.Shell.Design.VirtualTypeBuilder.InitializeFromType(ITypeResolutionService typeResolutionService, CodeNamespace ns)
at Microsoft.VisualStudio.Editors.SettingsGlobalObjects.SettingsFileGlobalObject.BuildType()
at Microsoft.VisualStudio.Editors.SettingsGlobalObjects.SettingsFileGlobalObject.GetObjectType()
at Microsoft.VisualStudio.Shell.Design.GlobalType.get_ObjectType()
at Microsoft.VisualStudio.Shell.Design.GlobalObject.GetHashCode()
at System.Collections.Generic.ObjectEqualityComparer`1.GetHashCode(T obj)
at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
at Microsoft.VisualStudio.Shell.Design.GlobalObjectService.TrackGlobal(GlobalObjectProvider p, GlobalType g)
at Microsoft.VisualStudio.Shell.Design.GlobalObjectService.GetGlobalObjects(Type baseType)
at Microsoft.VisualStudio.Design.Serialization.CodeDom.AggregateTypeResolutionService.GetTypeFromGlobalObjects(String name, Boolean throwOnError, Boolean ignoreCase)
at Microsoft.VisualStudio.Design.Serialization.CodeDom.AggregateTypeResolutionService.GetType(String name, Boolean throwOnError, Boolean ignoreCase)
at Microsoft.VisualStudio.Design.Serialization.CodeDom.AggregateTypeResolutionService.GetType(String name)
at System.ComponentModel.Design.DesignerHost.System.ComponentModel.Design.IDesignerHost.GetType(String typeName)
at System.ComponentModel.Design.Serialization.CodeDomDesignerLoader.EnsureDocument(IDesignerSerializationManager manager)
at System.ComponentModel.Design.Serialization.CodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager manager)
at Microsoft.VisualStudio.Design.Serialization.CodeDom.VSCodeDomDesignerLoader.PerformLoad(IDesignerSerializationManager serializationManager)
at Microsoft.VisualStudio.Design.Serialization.CodeDom.VSCodeDomDesignerLoader.DeferredLoadHandler.Microsoft.VisualStudio.TextManager.Interop.IVsTextBufferDataEvents.OnLoadCompleted(Int32 fReload)
Best regards,
Felix

Answer 1

Hello Felix,
The info seems tell us your project is corrupt. May I ask this question, will this error reproduce when you create a new simple project? This can be divided into two scenarios:
Scenario 1: The new project is also corrupt.
In that way, your Visual Studio may already corrupt. It's time for you to repair your Visual Studio from control panel.
If it still not work, try use some common steps below to fix:
Please open an administrative CMD window and navigate to C:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\IDE and run these commands:
1.devenv.exe  /safemode
2.devenv.exe  /resetskippkgs
3.devenv.exe  /installvstemplates
4.devenv.exe  /resetsettings
5.devenv.exe  /resetuserdata 
Scenario 2: The new project doesnot get this issue.
In this way, we should focus on this "The type
'System.Configuration.UserScopedSettingAttribute' could
not be found"
See here from MSDN to know how we can use it in our code:
https://msdn.microsoft.com/en-us/library/system.configuration.userscopedsettingattribute(v=vs.110).aspx
Check whether your code list something like below code and check whether you have missed anything here.
//Application settings wrapper class
sealed class FormSettings : ApplicationSettingsBase
[UserScopedSettingAttribute()]
public String FormText
get { return (String)this["FormText"]; }
set { this["FormText"] = value; }
[UserScopedSettingAttribute()]
[DefaultSettingValueAttribute("0, 0")]
public Point FormLocation
get { return (Point)(this["FormLocation"]); }
set { this["FormLocation"] = value; }
[UserScopedSettingAttribute()]
[DefaultSettingValueAttribute("225, 200")]
public Size FormSize
get { return (Size)this["FormSize"]; }
set { this["FormSize"] = value; }
[UserScopedSettingAttribute()]
[DefaultSettingValueAttribute("LightGray")]
public Color FormBackColor
get { return (Color)this["FormBackColor"]; }
set { this["FormBackColor"] = value; }
Or you can copy your project content to a new fresh project and rebuild your project with new settings.
Best regards,
Barry
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