Compiler Warning (level 1) CS1684 

Error Message

Reference to type 'Type Name' claims it is defined in 'Namespace', but it could not be found

This error can be caused by a reference inside one namespace referring to a type that it says exists inside a second namespace, but the type does not exist. For example, mydll.dll says that type A exists inside yourdll.dll, but no such type exists inside yourdll.dll. One possible cause of this error is that the version of yourdll.dll you are using is too old and A has not yet been defined.

The following sample generates CS1684.

Example

// CS1684_a.cs
// compile with: /target:library /keyfile:CS1684.key
public class A {
   public void Test() {}
}

public class C2 {}
// CS1684_b.cs
// compile with: /target:library /r:cs1684_a.dll
// post-build command: del /f CS1684_a.dll
using System;
public class Ref 
{
   public static A GetA() { return new A(); }
   public static C2 GetC() { return new C2(); }
}

We now rebuild the first assembly, leaving out the definition of the class C2 not to be defined in the recompilation.

// CS1684_c.cs
// compile with: /target:library /keyfile:CS1684.key /out:CS1684_a.dll
public class A {
   public void Test() {}
}

This module references the second module by means of the identifier Ref. But the second module contains a reference to the class C2, which no longer exists because of the compilation in the previous step, and therefore the CS1684 error message is returned from the compilation of this module.

// CS1684_d.cs
// compile with: /reference:cs1684_a.dll /reference:cs1684_b.dll
// CS1684 expected
class Tester
{
   public static void Main()
   {
      Ref.GetA().Test();
   }
}

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