Which version of the C++ source code did you use for this? The "official" releases before 0.7.0 were all built with VS 2003 and AFAIR didn't even build with newer version of VS.
Version 0.6.0, it did build, though I had to change one argument - runtime library I think, to /MD, and getting this warning:
1>cl : Command line warning D9035 : option 'clr:oldsyntax' has been deprecated and will be removed in a future release
I don't know the implications of changing the parameters I did, but the resulting dll worked fine (ACL, LW) so I figured things were OK.
Have you tried to compile the DLL from the 0.7.0 source code using VS 2008? I'm asking because I'm beginning to suspect that (my installation of) VS 2005 is the culprit. I've tried with Michael Goffioul's VS 2005 version of 0.5.0 and with Matthew D Swank's VS 2005 version of 0.6.0 and both failed as well.
Yes; it compiles with no warnings or modifications, but the same error occurs with Workbooks not having the Open (or any other) methods.
Iver