excel - Why do I get the 'fatal error LNK1120: 1 unresolved externals' when building (release) my C++ DLL developed for VBA?

I have developed a simple (no COM) C++ DLL for VBA (Excel) in VS 2008, which works perfectly on Win 10 and Excel 2016, as well as on Win XP and Excel 2003, both during debug and release. I have developed it following this example.

Now, jumping to the issue, using the same recipe and piece of code I have developed the same DLL, but in VS 2015. The debug and release versions for x64 work perfectly, but when I want to release the DLL for X86, it throws me the following error:

1>defFile.def : error LNK2001: unresolved external symbol "func_name"

Additional info, the project has only 2 files, as in the example:

Anyone has an idea how to get over this link issue?

My feeling is that, there might be a setting that I overlooked or skipped!
If you need the code or the settings, I will happily provide them, but they should be as in the example!

Thanks!