AWS EC2 PHP SDK SSL错误

Im trying to set an auto start and stop on my EC2 using PHP script. When im trying to run the script it turns out error like below,

Fatal error: Uncaught exception 'Guzzle\Http\Exception\CurlException' with message '[curl] 60: SSL certificate problem, verify that the CA cert is OK. Details: error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed [url] https://ec2.ap-southeast-1a.amazonaws.com/' .... ....

i've reinstalled the ca-certificates in my centos server. but the error persist.

Below are the specification details, PHP5.3. aws php sdk 2.8 centos 6.5

Anyone encounter this error before?