unmanaged calling managed fails in DLL

Hi,

I'm attempting to call managed code from unmanaged through a simple DLL interface. Microsoft docs claim (again and again) that this works fine but provide no examples. I set up an extremely simple console app that works fine (below). I put the same tiny bit of code in a DLL, set every compiler setting identical to the console app (CLR on), and it fails. It blows up deep in Windows with an undefined error.

I'm using VS-2010, .NET 4.0, Windows 7 64bit.
Here are the code samples:

Console app that works fine:
// hello.cpp : main project file.
using namespace System;
int write_msg(wchar_t *MSG1,wchar_t *MSG2);

#pragma unmanaged

int main()
{
      write_msg(L"Hello World",L"How is it going?");
      return (0);
}

#pragma managed

int write_msg(wchar_t *MSG1,wchar_t *MSG2)
{
      String^ msg1 = gcnew String(MSG1);
      String^ msg2 = gcnew String(MSG2);
    Console::WriteLine(msg1);
    Console::WriteLine(msg2);
    return 0;
}


Here's the DLL code that fails:
// This is the main DLL file.
using namespace System;
extern "C"
{
      void test_msg(wchar_t*,wchar_t*);
}
int write_msg(wchar_t *MSG1,wchar_t *MSG2);

#pragma unmanaged

void test_msg(wchar_t *msg1,wchar_t *msg2)
{
      write_msg(msg1,msg2);
}

#pragma managed

int write_msg(wchar_t *MSG1,wchar_t *MSG2)
{
      String^ msg1 = gcnew String(MSG1);
      String^ msg2 = gcnew String(MSG2);
      return (0);
}


When debugging, control gets to the unmanaged function test_msg(), and the arguments are correct. The error occurs when test_msg() tries to call write_msg().

A clue, perhaps. In the console app, I can set breakpoints on any line in the managed or unmanaged sections. In the DLL I can set breakpoints only in the unmanaged section.