My friend (Tummyrub) crashes when he logs onto my server yet no one else does

I am not sure why but my friend Tummyrub crashes every time he joins the server and yet its fine for everybody else.
He is on the server for ~1 second (Last time he tried he was on the server for 144 ticks)
I have told him to try updating java, installing minecraft, and reinstalling java.

my server ip is poco2.aternos.me
mcversion is 1.10.2

I'm pretty sure the console just had the normal disconnection message.
The picture of the crash report wasn't taken correctly but this is it.
Crash report
not sure if that link will work correctly for you.

Me and him have played on the wynncraft server.
I'm not sure if he can join other aternos servers, Ill have to ask him.