Cannot connect using public/private keys

I am running winscp on a Windows server using sftp on port 22. If I use a username and password to connect all is good. I have been trying to change my configuration to use public/private keys instead but connection always fails with an authentication error.
I am using the GUI to connect. I created by keys using puttygen and specified by private key in the GUI configuation and put my public key contents into .ssh\authorized_keys in the windows HOME folder of the user I am connecting as.
I am not using passphrase protection.
Every time, I get :
Authentication log (see session log for details):
Using username "svc_oracle".
Authenticating with public key "rsa-key-sf".
Authentication failed.

I attach the log file generated with Debug.

Where am I going wrong?

I should have mentioned that I cannot connect with public/private keys using putty either. I get the same error.
In puttygen, I generate RSA keys with 2048 bits.

What is an exact path to your authorized_keys?
Also did you check that the file is writable only by the respective local account?
See https://winscp.net/eng/docs/guide_windows_openssh_server#key_authentication