It might be the server but in general whenever this error happens and it can happen on any website, the way you can fix it is by clearing your cache and if that doesn't work then erase your cookies related to the site. Keep in mind you might lose a few settings this way but sometimes you got no choice. After you clear the cache and cookies try again and it should work.

If you don't want to clear your cache or cookies then just use a different browser and it should work. Usually this is a end user error and caused by some glitch somewhere on the users computer. If you tried all of this and it still happens then try the website on your phone using your cellular data. If you get the same error on your mobile, then most likely its the admin of the website which needs to fix the issue.