Problem with SSL certificate
There are some known issues with Drupal 7.x in some server configurations particularly around PHP 5.6 and OpenSSL 0.9x due to changes in how PHP verifies SSL certificates. Acquia has some notes about the cause and options (including a core patch to try to address some instances of the problem but read the whole article before considering that option).

On shared hosting you'll likely want to try the Alternative HTTP Client module to see if it resolves the notice.