how to fix "error C2872: 'IDictionary' :ambiguous symbol

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C++/CLI

Hi All,
I need to use IDictionary in my project. When I add this compiler does not like it and report an obvious error
“error C2872: 'IDictionary' : ambiguous symbol” . However if I create a new sample project compiler never reports any error

Below is the code snippet

Temp.h
#pragma once
#using "System.dll"

using namespace::System;
using namespace::System::Collections;
using namespace::System::Collections::Specialized;

public ref class MyCollection : public NameObjectCollectionBase  {

private:
   DictionaryEntry^ _de;

   // Gets a key-and-value pair (DictionaryEntry) using an index. 
public:
   property DictionaryEntry^ default[ int ]  {
      DictionaryEntry^ get(int index)  {
         _de->Key = this->BaseGetKey( index );
         _de->Value = this->BaseGet( index );
         return( _de );
      }
   }

   // Adds elements from an IDictionary into the new collection.
   MyCollection( IDictionary^ d )  {

      _de = gcnew DictionaryEntry();

      for each ( DictionaryEntry^ de in d )  {
         this->BaseAdd( (String^) de->Key, de->Value );
      }
   }

   // Removes an entry with the specified key from the collection. 
   void Remove( String^ key )  {
      this->BaseRemove( key );
   }

   // Removes an entry in the specified index from the collection. 
   void Remove( int index )  {
      this->BaseRemoveAt( index );
   }   
};

I am using VS2012