Syncing Yahoo Calendar Won't Sync to I Mac

I set up my iMac to sync with my Yahoo account. In the settings screen I chose the Yahoo option and properly entered the account and password. I checked the boxes for mail, contacts and calendar. The mail and contacts boxes remain checked but the "Spinning Wheel of Death" spins in the Calendar box and eventually I get a dialog box that says "A secure connection couldn’t be established". The mail and contacts are syncing. Tried deleting and re-trying set up with same result. Stumped!!!!!