Minecraft won't launch after changing username and logging in/out multiple times

I changed my username on Minecraft, and I tried logging out and back in but it won't work. I tried multiple times but I still can't go on any servers.

Solution 1:

I'm pretty sure that they now prefer you to use the email address for your account and not the username.

This article details which to use: Do I log in with my email or username?

You log in with your email address if you purchased Minecraft after November 2012, or migrated your username to a Mojang account.

You log in with your username if you have an older Minecraft account, and have not yet migrated to the new account format. You can migrate to a Mojang account from the Mojang accounts page.