See if this helps
by Maratdu - 8/31/11 1:15 PM
Had the same problem, then found one note among hundreds in a similar thread that solved the problem. It was so simple it was embarrassing after several days of frustration.
When one enters the password by choosing characters on the screen, there is a small box near the bottom of the screen on the left(?) (sorry, I am not at the screen so this is from memory), at which one chooses whether the phone-type entry is a number or a letter. I think the default is number. I was just entering the default and not noticing the character choice, and I had mixed numbers and letters in my password. When I tried the fix that was suggested (making the choice of letter or number before each entry), it worked perfectly, and it has worked ever since.