Hello Yuksel,
Plese, make sure that you start the Desktop Connection for SAP CRM only when the SLS certificate is already enrolled. I am not sure that the certificate will be displayed in the drop-down if you first start the solution, and then enroll the SLS X.509 certificate, and then look back at the solution.
If you are sure that the SLS X.509 certificate is enrolled first and is available in the certificate store, and then you start the Desktop Connection for SAP CRM and you don't see the certificate, Please, create a CSS message on the SAP CRM component, explaining that you are trying to configure SSO based on X.509 certificates. Explain that you are facing the following problem: The X.509 certificate of the user (available in the certificate store of the user) is not properly displayed in the drop-down for selection during the authentication process.
Regards,
Donka