Help! Can't join friend in multiplayer

(SOLVED) Friend loaded an old save and invited me in. Managed to connect this time, then they reloaded the current save and it worked!

Whenever I try to join my friends' game, it comes up with the error message : ERROR JOINING : Can't join game right now!

Is this happening to anyone else? We played last night and everything was fine...

I can't seem to find anything about this particular error, and I've tried multiple things already that haven't worked sadly. ):

Hoping someone has a solution