Cannot Upgrade Network due to SSL

Hi,
I have problem upgrading my network. I set to use SSL on admin area. And its working fine. I also use "Wordpress HTTPS" plugin. In WP-config, i force to use Force SSL Admin.

Whenever I click on upgrade network on my superadmin, it show this error.

Warning! Problem updating https://mysite.com/site3. Your server may not be able to connect to sites running on it. Error message: SSL certificate problem, verify that the CA cert is OK. Details: error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed

I can login into site3 admin without problem. The site3 is the first site it try to update and failed. I presume others will be the same too.