Unable to sign Logout Request

Team, We require to send Signe Log out Request to our partner application. we are able to implement SSO with them, but when we send log out requests they expect Singed Logout Request. when we tried to sign the Logout request with the certificate they provided us we are getting the below issue. //sign the logout request with partner certificate logoutRequest.Sign(X509PartnerCertificate); logoutRequest.SendHttpPost(Response, logoutUrl, relaystate); //sign the logout request with partner certificate ComponentPro.Saml.SamlException: Unable to generate XML signature. ---> System.Security.Cryptography.CryptographicException: Signing key is not loaded. Thanks Ashish