I can't join my friend's world.

Hello! I am a new player and just bought the Minecraft! When I wanna try to join my friend’s world. When downloading the pack or something of it, it always error! I am sad because it and I rejoin the world until 5 times but it didn’t work! Its only my account, but my friend account when joining me its okay, he can join fine but me always errors! Thank you. May this post can be responded and affected at bug fix!