Hey LilSkittle,
That "restart your game and launcher" message usually pops up when you're trying to use a cracked alt on a non-cracked Minecraft server.
It's important to remember that cracked alts aren't real Minecraft accounts, they're basically just a username that you can use on a cracked server (a.k.a. an offline-mode server), where you don't need a genuine Minecraft account to play.
To join a regular online-mode servers, you'll need to use a real Minecraft account instead. This is typically referred to as a premium alt on the Wurst Wiki, for example on this page.
Hope this clears up the confusion!