One problem that sometimes occurs is that, by default, the iPad autocapitalises the first letter of the first word of what it considers to be a new sentence. If your password begins with a lower-case letter, check carefully as you type it in that the iPad is not automatically changing it to upper case. If it is, then simply hit the shift key to cancel shift before typing in the first letter.
I've also moved this thread to the Help section, where I think it will receive better attention, in case my suggestion doesn't work.
Tim