Failed to load designer

I'm having this problem:

When I try to access Design View, I receive this message:

Failed to load designer. Check the source code for syntax errors and check if all references are available.

ICSharpCode.FormsDesigner.FormsDesignerLoadException: System.ComponentModel.Design.Serialization.CodeDomSerializerException: The variable 'DateTimePickerFormat' is either undeclared or was never assigned.

   at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.Error(IDesignerSerializationManager manager, String exceptionText, String helpLink)

   at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializeExpression(IDesignerSerializationManager manager, String name, CodeExpression expression)

   at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializePropertyReferenceExpression(IDesignerSerializationManager manager, CodePropertyReferenceExpression propertyReferenceEx, Boolean reportError)

   at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializeExpression(IDesignerSerializationManager manager, String name, CodeExpression expression)

   at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializePropertyAssignStatement(IDesignerSerializationManager manager, CodeAssignStatement statement, CodePropertyReferenceExpression propertyReferenceEx, Boolean reportError)

   at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializeAssignStatement(IDesignerSerializationManager manager, CodeAssignStatement statement)

   at System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializeStatement(IDesignerSerializationManager manager, CodeStatement statement)

   at ICSharpCode.FormsDesigner.FormsDesignerViewContent.LoadDesigner()

   at ICSharpCode.FormsDesigner.FormsDesignerViewContent.LoadAndDisplayDesigner()

   at ICSharpCode.FormsDesigner.FormsDesignerViewContent.LoadInternal(OpenedFile file, Stream stream)

   at ICSharpCode.SharpDevelop.Gui.AbstractViewContentHandlingLoadErrors.Load(OpenedFile file, Stream stream)

I tryed every thing and I still don't know how to workaround it. This is the code that trigger the issue:

this.dateTimePicker1.Format = DateTimePickerFormat.Custom;

It runs like a charm, but Design View gets this error.