Log in to the site using your nickname and password. Click on "My profile" in the top navigation menu, or click on "User Menu" in the left top corner. On the bottom of opened page you will see "Allow rating", choose the wanted option. Then click "Save Changes". It's done!
I had the same problem.
If you have a router from TP-Link, D-Link, ASUS or maybe a router produced by some other companies
then this is a problem with a router.
There are two ways to solve this problem:
1) Upgrade firmware for your router. You may download the last version of firmware
from website of the manufacturer of your router.
2) Change "MTU" value to "1400" in your router settings.
This option is located in "IP Config" -> "WAN & LAN"