Modded server lets one person in, doesnt let the other

Im trying to run this modded minecraft server for me and someone and it all seems to work, i connect everything works just as fine but when he tries to connect, he goes in for a second, then it says connection lost and he disconnects. We are 99% sure its not the connection, as other minecraft servers work, we just dont seem to know how to fix this problem

Update:

Tried without mods, the problem persists

Screenshot on his screen or on the console?