Thanks @Lucius and @LoyceV.

I'm sure the private keys were correct, as I used copy and paste, and was very careful throughout the entire process (and also, I found others had the same problem, not just in this forum, but also in the comments of the guide).

However, it seems the consensus is that it's unnecessary to bother doing it that way anyway, and that I can import the seed, just as I always thought. Just wonder why that guide recommends doing it with private keys, when that's much more fiddly... 

I'll give importing the seed a go, and report back.

Thanks for the help.