You'll see this error message when playing in multiplayer mode sometimes.
To fix it, try all the following:
1. Restart your Minecraft client.
2. Restart your computer.
3. Unplug and reconnect your router.
4. Download a new version of the Minecraft.exe file.
5. Ensure Java is up to date.
If none of that helps, try the suggestions on this blog post: http://www.minecraftman.com/internal-exception-java-net-socketexception-connection-reset/