The National Archives of Ireland is experiencing server problems. These seem to have started yesterday and are on-going, so access via the main website (www.nationalarchives.ie) and the dedicated Genealogy section (www.genealogy.nationalarchives.ie) is very hit and miss. I was able to access and search the census last night on the genealogy site, but this morning I can't get past the census 'home' page.
The National Archives tell me they became aware of the problem yesterday when emails stopped getting through and were bouncing back to senders.
The IT department is working to fix the problem. No time scale yet, but it is in hand.