I received the 504 error gateway timeout without knowing what is going on. Maybe because I create too many sub domains with plugins installed or what.
Here are the explanation from source : http://pcsupport.about.com/od/findbyerrormessage/a/504error.htm
HTTP Error 504 - Gateway Timeout"
The 504 Gateway Timeout error displays inside the Internet browser window, just as web pages do.
Cause of 504 Errors
The 504 Gateway Timeout error is an HTTP status code that means that one server did not receive a timely response from another server that it was accessing while attempting to load the web page or fill another request by the browser.
This usually means that the other server is down or not working properly.
The 504 Gateway Timeout error is usually a network error between servers on the Internet or an issue with an actual server, meaning the problem is not with your PC or Internet connection.
Even though the issue is not yours to troubleshoot or resolve, there are a few things you can do:
Retry the web page by clicking the refresh/reload button or trying the URL from the address bar again. Even though the 504 Gateway Timeout error is reporting an error outside of your control, the error may only be temporary.
Trying the page again will often be successful.
Come back later. Since the 504 Gateway Timeout error message is an issue with the web site's network or a server that it communicates with, everyone visiting this site is probably experiencing the same problem as you.
Chances are an issue like that has already been brought to the attention of an administrator at the web site and someone is working to resolve it.
If you can't wait any longer for the problem to be resolved or if you'd like to help out, you may want to attempt to contact the webmaster or another website contact yourself and advise them of the 504 Gateway Timeout error you are receiving.
So it could not because of sub domains. But I already delete some of them. hmh….