@Clark3loyd, I doubt there will ever be a final product as it's quiet unlikely that xbmc will integrate spotyxbmc into the official release soon :/
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StefanK, if you don't post the errors, there is no way we can help you :p
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bigmacpaddy, I never compiled anything on windows, so I might really not be the best person to help you :/
But I will give it a try.
The error you got is a linking error, that's mean the linker is gathering all the compiled code into one big file.
These unresolved external symbol error means that the linker can't find the actual code behind the header definition you provided him.
It seems that the compiled code the linker can't find is the Addon_music_spotify, which should be in xbmc/music/SpotyXBMC.
If I got this error on linux I would give a look at the Makefiles (or windows equivalent), to make sure that the files are included (like in xnmc/music/Makefile).
And make sure Addon.music.spotify successfully compiled in the first place.
Maybe you could try to compile the 12.1 version, make sure it compile, and then try to spot any differences between the two versions.
It's very likely I missed something as I am really new to this :/
Anyway, thank you for looking at it