Problems with Hamachi, Mods and other things.

Really, i don't know if this can be published here; If it can't, tell me and i will remove it before than a mod.

Hello everybody, Here i come next to search and search in Internet and...(like anybody in this forums) I DIDN'T FIND ANYTHING. Ok, my problem: My friend and me (No Premiums, Sorry, We don't have credit card :( ) tried to play in my world using Lan Server and Hamachi, but when he tries to enter in my world, he receives the message:

Failed to login: Invalid Session(Try Restarting your game)

That is the message when you try to play in Premium Server if you aren't Premium. We don't use Bukkit, Spigot or original minecraft_server.jar, so Server.Properties DOESN'T EXIST. We are in minecraft 1.8.9 With Forge and Thaumcraft 5.1.6 If you can help us, Thank You very much. Sorry grammatical and orthographical mistakes, My lenguage is spanish