Update 5 Dec: Looks like most users are back working, although there are still some intermitted problems with Three servers.
Many users are reporting today that they are getting failed login for Three webtexts. Three have stated that they are looking into this on boards.ie.
I have looked into my own accounts and get the same access denied messages when I try and login via Chrome or Safari on my desktop.
This is not a problem with Jelly SMS, and can only be resolved by the operator.
Please post here if you are also experiencing this problem.