A technical problem appears to have hit the National Library of Ireland's RC Registers website this afternoon.
When you identify the parish you want to search, you are erroneously told that the NLI doesn't have any available registers for the area (see example below). I've checked a dozen parishes and all of them return the same message, but it's possible there are others functioning correctly.
The Library IT team is working to solve the problem.
UPDATE, Friday 7 July, 10:20am: Problems solved. Site seems to be functioning properly again.