The following things may help.
- Close all uploads, downloads or programs other than the ones used to play the game.
- Don’t make your farm too big.
1. Clear your computer's cache and cookies. How you can do that, is described here: https://www.facebook.com/help/?page=185360664848864
2. Try using a different browser (I've heard Mozilla Firefox or Palemoon works well. also try Google Chrome)
3. Make sure you have the latest version of your browser and Flash Player.
4. Make sure you have disabled your pop up blocker.
5. Have you tried to enable Cache or cookies from third party? Go here (viewforum.php?f=13
and check out which ever browser you use (Accepting cookies to send request&receive gifts))
6. Reset your router.
7. Try another account on your computer
8. If possible, try using a different computer.