Please excuse the frustrating undertones as I have attempted to get this set up correctly multiple times to no avail (possibly and most likely due to my ignorance, but also
I think the problem is that you ssh client (windows or linux version) is not finding the key file. I had the same problem and solved this way:
I added a file name config in ~/.ssh with following content:
IdentityFile ~/.ssh/rafael.nicoletti@corporation
In every location i want to access my git servers, i just copy those files in my %HOME% folder
You can also put the some things like this in config file:
IdentityFile /d/identity.key
IdentityFile /e/identity.key
IdentityFile /f/identity.key
IdentityFile /.../identity.key
So the config will look for keys in removable medias.