Okay, I tried replacing all province colours by those that are definitely 'legal', and since you mentioned it, I tried another thing: When I started working on this map, I had first saved the provinces.bmp in 32 bit - and it loaded. Sure, the map in-game was black and without provinces, but it actually took me to the main menu.
Now, I tried changing it to 32 bit again, hoping that this would possibly keep the game from trying to check whatever it is checking for an infinite amount of time now, but: negative. It still keeps loading "initializing maplogic..." (or "if you can read this, you have failed...", as I call it) forever.. So maybe the problem is to be found somewhere else entirely?
Then again, the problem started the second I re-saved the map as 24 bit. I'm really getting lost..