While playing Minecraft, I changed my name and now I can't access any servers. I've tried logging out and back on, but it still won't work. I'm afraid that I may not be able to play Minecraft anymore...
- The Session ID that your client is using, might be out of date.
Try logging out & in in the Minecraft Launcher.
If that does not work, you might want to go to your .minecraft folder (located at %appdata% on Windows, and in your /home/ directory on Linux) and delete the file called 'launcher_profiles.json'. After this, go to your launcher and log in.
You are playing in an old version (specifically in a lower one than 1.7.6, not including 1.7.6) or with mods.
You have been banned from the servers, or if they are whitelisted, you are not whitelisted anymore.