unable to add client certificate in connection

I have a ftp server configured to request client certificate.
I'm trying to add to the client connection one of my client certificates but I don't know how to do it.
In my connection (FTP over TLS)I select Properties -> Connection -> SSL/TLS and select Enabled in the Client certificate panel.
Then I click the button Cert Manager to select my client certificate but when I click my certificate and close the dialog no certificate is selected.
I need to use one of my certificates (don´t want to create a self-signed one)
What am i doing wrong?

Thanks in advanced.

You need to select the certificate from the certificate combo box. Does your ceritifcate show there? If not, it does not have a private key and it cannot be used as a client certificate.

Thanks.
I'll try to create a .pfx that includes the private key.