Not being able to get into the game

Every time i try to launch league it works fine until i get to the main menu. A black screen shows up and pops up the message "There was an unexpected error with the login session. Please try again." This all happened yesterday when i wasn't able to launch the game. I even tried restarting my computer and it still doesn't work, but having a friend log into my account dose. I don't know why this is happening but i would just like to play some league. Thank you for your time.