ssh-add does not delete identities

["Eduardo M. Suárez Santana"]

$ echo $SSH_AUTH_SOCK
/tmp/gpg-uQE5lB/S.gpg-agent.ssh
$ ssh-add -l
1024 05:23:57:xx:09:2e:06:9h:bb:7f:fb:18:f9:fa:8b:21 myfile (DSA)
2048 16:be:06:ff:72:7c:fc:63:74:1c:97:f3:xx:2f:87:c3 myotherfile (RSA)
1024 8d:1d:73:77:ce:xx:d2:82:93:ee:be:c1:3b:0f:25:c7 yetanotherfile (DSA)
$ ssh-add -D
SSH_AGENT_FAILURE
Failed to remove all identities.

What am I doing wrong?