Trying to SSH into my Arch Linux Laptop, and this message pops up
 

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
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IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
********************************************************* (I'm not sure if I should expose it or not)
Please contact your system administrator.
Add correct host key in /home/theif519/.ssh/known_hosts to get rid of this message.
Offending RSA key in /home/theif519/.ssh/known_hosts:5
remove with: ssh-keygen -f "/home/theif519/.ssh/known_hosts" -R 192.168.1.7
RSA host key for 192.168.1.7 has changed and you have requested strict checking.
Host key verification failed.


I followed this guide...

https://wiki.archlinux.org/index.php/SSH

And it got it working. When I tried doing it *With X11 Forwarding* this happened. I have two questions actually, 1. How do I enable X11 Forwarding from Ubuntu? I tried SSHing into it with X11 Forwarding and verbose, but... It wouldn't allow me, it said Gtk-WARNING or something, do I have to change my SSHD config files? If so, how *Do I do it*, what *Do I do*, and where is it? Second question is, I do know that my Laptop is safe, so I want to know how to give it permission to SSH.

I got X11 Forwarding from my Laptop, but I still can't SSH into my Laptop

I have got this message before myself, when I tried to SSH into one of my machines through two distros that were dual-booting on another machine, but got the same IP address from the router. I believe this problem can be solved by just creating a pair of SSH keys and putting them on each of the machines, so that there is no 'identity crisis'. You can follow this guide:

https://wiki.archlinux.org/index.php/SSH_Keys