Just a weird little datum that may help some:
Normally, when you enter a password and hit Enter, it will do the same as if you click on the OK button on the form. But recently I have twice (once on a web site and once in a Windows dialogue) found examples where the password seemingly didn't work... except when I used the mouse to click OK instead of hitting Enter, it did work. I can't say why.
Just another thing to try if you know you're using the right pw, but it's no go.