I've been throwing everything away except one class which has only an  
empty constructor. When I build the .NET DLL now there is basically no  
code inside - but the problem remains.

Going once again through the project configuration I would guess that the  
dependency on an unmanaged library causes the problem. Although the .NET  
DLL currently does not call any functions in the unmanaged DLLs it depends  
on I still have to add a dependency to the project configuration although  
this library is only used by the unmanaged DLLs the .NET DLL depends on.  
If I don't add the dependency I get "unresolved token" and "unresolved  
extern symbol" errors. If I do the errors disappear and only a warning  
"unresolved typeref token ...; image may not run" remains. That said I do  
get a DLL then but it seems to be faulty.

Although I don't know if I'm on the right track I wonder if there is  
anything to take care of when a managed DLL depends on an unmanaged  
library?

Boris

I found out what causes the problem (which doesn't mean though that I have  
an idea how to solve it) and can now provide a reproducable test case. You  
must have installed Boost 1.34.1 (see http://www.boost.org/) and add this  
code to a C++/CLI project:

#pragma once
#include <boost/thread/mutex.hpp>

#using <mscorlib.dll>
using namespace System;

namespace MyNamespace
{
  public ref class MyClass
  {
    public:
      MyClass() { }
  };
}

Including the header boost/thread/mutex.hpp makes it impossible to load  
the DLL (yes, including is enough - no need to use any code from that  
header). I probably have to submit a bug report to Boost (or Microsoft?).

Boris