have you looked at exported symbols in dll? it may be C++ from what you said(lib not designed for C++?), so you can try extern(C++) on D side instead extern(C). or add manually #ifdef __cplusplus and extern "C" on lib side(if its not that big of course).
First of all: I started with a C++-dll and tried to declare the functions with extern (C++) --> did not work. Then I switched the compiler to C. As VC++ still uses only C89 as standard you can imagine there is NOTHING C++-ish that could have survived. I also tested this DLL in a C++-application (static) and it worked like a charm.
ALSO:
As i suspected that some things written by me could be responsible for this, I build a test application with three functions (Test, Test2,Test3), got myself the D-.lib for statical-linking (implib-Dmd) and tried that one out. The result: Error 42.
So, actually I am trying to get a DLL containing three single-line test functions to work. What I have already achieved is to load it dynamically, and it worked (Derelict.Util.Loader.SharedLibLoader Class). As I also use the Derelict-packages, I may intend to build a custom loader class as a work-around.
