Comment 23 for bug 187127

auth.log is a good idea :) There I found the problem for my above described problem

| Jan 23 18:10:12 ax-tge gnome-keyring-daemon[6440]: couldn't find or load public key for private key
| Jan 23 18:10:12 ax-tge gnome-keyring-daemon[6440]: user denied this prompt previously, skipping prompt and automatically denying

I had in my ~/.ssh directory an old private key for which no public key was in the same directory. This seems to confuse the gnome-keyring-daemon. After deleting the old private key my problem disappeared!