Ah shoot.
I logged on the Android BBM app, couldn't sign back into BBM on my Classic.
Later, I signed up for BBMe because BBM is getting shut down on Android.
After that, I tried signing in on BBM on my Classic, and it worked perfectly.
Finally, I switched to BBMe on BB10 because I subscribed to the trial, and it won't log in and I can't go back.
Any ideas for how I can fix this? I contacted BBMe support, and they just sent me a useless link.