I have been trying to create some more test customers to check out my shipping modules, (I have previous created two test customers successfully) but now the following message shows up in the browser when I submit the information:

Not Acceptable
An appropriate representation of the requested resource /index.php could not be found on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request

Can anyone tell me what has happened,