What is the cause of Error Code 118, and how can I resolve this?

Above is a screenshot of the error I am getting in my Steam application. It says:

"Unable to connect to server. Server may be offline or you may not be connected to the internet."

I have a connection to the internet and it's working properly, I have no clue what might be the cause of this problem but I can visit the site when I use the "cache" option instead as below;

Any idea what might be the fix for this?