Custom controle not working (VS2012)

[Precious roy]

Hi

i'm trying to add a custom control to my project. after i compile i can see it in my toolbox but when i add it VS gives me this error:

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Microsoft Visual Studio
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Failed to load toolbox item 'myPanel'. It will be removed from the toolbox.
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OK
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my code for the panel

#pragma once
using namespace System;
using namespace System::Windows::Forms;

public ref class myPanel : public Panel {
public:
	myPanel() : Panel() {
		SetStyle(ControlStyles::DoubleBuffer, true);
		SetStyle(ControlStyles::UserPaint, true);
		SetStyle(ControlStyles::AllPaintingInWmPaint, true);
	};
};

if i manually edit the code and run the program, then the panel works just fine.

myPanel^  mPanel = gcnew myPanel();
mPanel->Dock = System::Windows::Forms::DockStyle::Fill;
this->toolStripContainer1->ContentPanel->Controls->Add(mPanel);

any idea what i'm doing wrong?