Steven Mitchell says:

The problem with the ssh key was including just enough of the file. 
The ssh public key file was 5 pieces: 
 
header at the top (ssh, etc) 
a single space 
the key 
a single space 
a user:domain 
 
First tried to copy/paste just the key, and then the whole  
thing--neither worked. 
 
Then copy/pasted the header, single space, the key, leaving off the 
second single space and the user-domain statement.  That worked.