I have just gotten my internet started up at my house, so I tried going on SA:MP. I noticed that 0.3c was installed, so I installed 0.3d. After doing so, I attempted to log in, and I got the message "CONNECTION REJECTED: Incorrect version."
I have never had this problem, so I do not know anything about it. I do not want to reinstall SA:MP or anything yet, without knowing what causes this problem.