SSH with Windows Vista + Putty + GitLab

I am very new to GitLab and just set up an account and an empty repository. I added my public key (which I use successfully elsewhere) and tried to SSH in using Putty.

GitLab sees my key file and prompts me for the password. Once I enter the password the session (Putty) is closed automatically.

A review of my putty log reveals:

Using username “git”.
Authenticating with public key “Alysa Selby Key”
Passphrase for key “Alysa Selby Key”:
Server refused to allocate pty
Welcome to GitLab, Alysa Selby!

Can anyone advise as to why the session closes despite recognizing who I am?