The following information is also available in the form of an infographic.
The browser cannot find the page - this is a problem with the domain (e.g. expiry) or DNS server.
Timeout - it seems that the page is loading but it takes a lot of time and nothing is displayed.
Error message - the server displays a three-digit error number and its description (see Server Error Codes below).
The page is displayed incorrectly - e.g. some content or images are missing or everything is shifted.
Functionalities do not work - e.g. a contact or registration form.
The most common http error codes and their meanings.
401 Unauthorized - authentication has failed or not yet been provided.
403 Forbidden - the request was a legal request, but the server is refusing to respond to it.
404 Not Found - the requested resource could not be found but may be available again in the future.
500 Internal Server Error - a generic error message, given when no more specific message is suitable.
502 Bad Gateway - the server was acting as a gateway or proxy and received an invalid response from the upstream server.
503 Service Unavailable - the server is currently unavailable (because it is overloaded or down for maintenance).
Human error - the root of application and system errors and less frequently hardware errors.
These are unintentional failures which are most easily repaired.
Random - impossible to be foreseen, e.g. a failure of a new hard disk from a renowned producer.
These also result from natural catastrophes, burglaries where hardware is stolen etc.
Intentional - these are usually planned shutdowns where it is impossible that each and every user is informed.
However, these are also hacker attacks.
Hardware wearing out - mechanical elements (e.g. traditional hard disks) have a limited life cycle.
As is the case with people - some die earlier and some die later.