Hi,
I am attempting to install the latest l8, but I am stumped by this error:
The only reason I can think of is that my litium package source is incorrect. But I don’t think so?
Source looks correct and I tried installing the template just fine. Could you try deleting the source and adding it again? It might be that your credentials are incorrect (same as on Docs).
I think I used the correct password, but I’ll give that a shot! 
That was indeed the problem! Thanks!