RestCleint: SSL ceritificate not verified; not able to validate the **AlphaSSL certificate**

ERROR ... caught RestClient::SSLCertificateNotVerified: SSL_connect returned=1 errno=0 state=SSLv3 read server certificate B: certificate verify failed:

I have update openSSL and did all the possible ways available in internet. Still not able to validate the AlphaSSL certificate. Please let me know the possible changes to solve this issue.