Well, this started happening a while ago, but I kept forgetting to post.
Basically, users register, enter a password, go to login, enter that same password, and it says it isn't correct. So they either have to get their PW sent to them, or ask an administrator to change it. But the thing is, when I tried registering another account, it worked fine... And I do know that it's happening and it's not just entering wrong password, because almost every single member had that problem.
This happened to me with 2.2.4, what version are you running?