Cant login because invalid session

This probably is one of the most simplest errors to fix, but have no idea of how to do it, it just that, i try to login with IP or DynIP, but keep sending that same error, anda obviously i try restartin but didn´t work
Another thing to say, is yesterday a friend made a aternos server and i could enter her server with no problem, now i did the server and i cant enter
Any ideas?

I already said in my message that i did it, that's why i'm asking for a solution since that didn't work >. <