I dont think people can join my server. HELP

[fearpb]

Ok so, i can join my server. Its a public server named "I am the walrus".
Its up and running. I can join it. But whenever my friend tries to join it. His screen goes black like its going to load or it minimizes to his top right corner of the screen. And then goes back to the login asking him to login again.

Ive search the forums up and down for help with this problem. But I have yet to find any.

If you wouldnt mind and trying to join my server to see if it does it to you then please try. And throw me some feedback on what you think the problem is. I would greatly appreciate it.

Thanks ahead of time,
Fear