It has turned out that the crash bugs are caused by the MSVC .NET compiler. I could fix the menu crash bug there, but not yet the crash when starting a game.
I have therefore compiled d2x-w32 with MSVC 6 and SDL 1.2.7 (1.2.8 doesn't compile with MSVC 6) and uploaded that program version. It doesn't have these crash bugs.
Nevertheless I'd need some help by somebody having the start game crash bug to make d2x-w32 work with MSVC .NET.