Strange Key, maybe bad REX.

Hey guys! I'm not sure if this is the exact place to post this thread but there really isn't a subsection for music theory. And maybe thats ok because this really isn't a BIG theory question. Ok, I'll cut to the chase. I have this weird REX file called 'nd_bs120_decimate_A#m.rx2'. So basically, it's telling me that the key of this particular REX file is in A#minor. Now I know there is a key of A-minor; and I know there is a key of A-major. But as far as I know there isn't a key of A#minor on the circle of fifths. Am I missing something or, did someone just mislabel this REX? Because it's super annoying trying to compose stuff around this REX without know the key. :brkwl:
There is a key of A# minor. It is more commonly thought of as Bb minor. But that is just an enharmonic name (different name for the same note(s)). I say more "commonly" for no reason other than that some keys are more commonly used than others. Key signatures are not a democracy. They are not all used equally :) Some are easier to play in than others on certain types of instruments.

Think of it as Bb minor if it helps you understand it better.
Thanks Eli! That was driving me INSANE. It's a little annoying that they just don't call it Bb-minor instead of A#minor. But the note C# is the same as Db, and I get that. That was a little annoying at first but it made sense. I just didn't think that Keys could also have enharmonic equivalents. But It makes sense now to me too. Thanks again, Eli. I'm off to go write music!