I've used the following FTPS: CoffeeCup, Internet Explorer, Foxfire, FTP Commander, WSFTP_LE and Smart FTP and a few others I can't even remember.
Thus far I've liked CoffeeCup the best. However I'm too cheap/poor to pay money for an FTP so I only have CoffeeCup for 30-60 days after the new version comes out... I probably just buy it. So right now I'm using SmartFTP. I like it a lot, not as much as CoffeeCup, but nearly.
So I vote SmartFTP since you can use it LONG after the trail has ended and the one pop up you get asking you to buy it before it starts it trivial. Less then 2 seconds you've hit OK and enter the program.
But if you are having trouble signing in I would talk to the admins and make sure it isn't your account.
Forest Gump once said "Stupid is as Stupid does." I say all the time "Stupid people really shouldn't be left unsupervised at a bus stop."