First, we need to explain your browser's Cache, because your browser aims to give fast service, it stores a copy of certain sites in a memory called the cache, and when you load a page it sometimes loads the copy from the Cache.
Our system is real-time based software, it constantly updates and the previously stored copy of our site is no longer relevant. This can cause a Server Error.
Your browser is supposed to clear the cache by itself, but sometimes it isn't fast enough so you need to do it manually.
How can I do it?
First Make sure you are using the Chrome Browser, this browser is the most compatible with new software and it usually has better Cache cleaning system.
Clear your Cache Manually
This sounds way harder than it actually is, however it is very easy to do.
Just follow the steps in this article: http://help.exportyourstore.com/customer-support/emptying-your-cache
Log In And Log Out
If all the rest have failed, this is sure to work, just sign out and sign right back in, this should fix any problem that may occur.