This is likely caused by an out dated plug in. You should try updating your flash player via adobe web site http://get.adobe.com/flashplayer/ If that doesn't work, you'll have to contact Zynga support via https://www.zyngaplayersupport.com/ click your game; then on right hand side there's a red "?Get Help" click on this then either mail them or use chat.
Answers & Comments
This is likely caused by an out dated plug in. You should try updating your flash player via adobe web site http://get.adobe.com/flashplayer/ If that doesn't work, you'll have to contact Zynga support via https://www.zyngaplayersupport.com/ click your game; then on right hand side there's a red "?Get Help" click on this then either mail them or use chat.
Try to sign in again on the next day maybe it will work again.