I also have a very similar problem as what
@Pangaea was describing. I also recently bought CivIV complete from that GOG.com sale (only costs $7.50, until feb 25th I think, btw). But I am using windows 10. The game runs fine (tried warlords, BTS, vanilla and colonization). But, when trying to load the BUFFY mod, I get the exact same message, that HOF submissions will not be possible, but I can still proceed to load the mod and it appears to work completely, afaik.
What is more frustrating to me is that I cannot get Map Finder to work at all (I've tried for hours and read all this thread and many parts of other threads). I wonder if this is the same root issue, particularly as it does show it as a 'registry' error message. Problem is, this is the first copy of Civ4 that I have ever had (first time I've ever tried to play it) and so I don't have any type of old registry to copy, nor would I know exactly how to implement it correctly if I did. So I'm wondering if I can get more details from Pangaea or someone else who may have resolved this on windows.
Things I have tried are changing all the files in my install folders to read only and giving 'users' full control to all the access, in both these places (default places the GOG install client placed them):
C:\Program Files (x86)\GOG Galaxy\Games\Civilization IV Complete
C:\Users\<my_user>\OneDrive\Documents\My Games\Beyond The Sword
I have also made all the Exe files 'run as admins'. And tried a couple compatibility options for the Civ4_Map_Finder.exe and none of that helped, probably no surprise.
Some other minor things I've tried is installing the Map finder in many many different folders, and even the BUFFY mod in both program files and Documents (loads fine from both, but still always get the warning and fail for Mapfinder). Here is a screenshot of the map finder error:
Another issue I've had that maybe I'll try to resolve further if I get the major ones resolved: I couldn't get the mod to load by default or with a modified shortcut as the instructions here outline:
http://hof.civfanatics.net/civ4/mod.php?show=mod#buffy_download
I couldn't ever get windows to accept the shortcut as valid, nor could I find any .ini file that looked for sure like one that I could add to to get the mod to load by default. Both of these issues, or particularly the latter could well be due to GOG changes (GOG has some custom looking ini files in there and there is no "CivilizationsIV.ini"). I'll probably post a separate reply on this later, some parts of the instructions from the mod site seemed conflicting and confusing to me, as well.
You'd think if the GOG folks are going to bother modifying the install files so much at all, they would test that their version works with basic things like this, since this is by far the most popular Civ community. Right? haha... Meh