Couple of things to try:
* open up firebug and see if there are any errors in the console
* check the server error logs to see if the error is logged there.
Its a server level error, so its probably permissions at a guess.
I'm going to guess there's an apache config error, as that likely is being submitted to a "page not found" (404) which is why you see that. Make sure DNS is working and the apache config is correct.