Did you perhaps mean that you downloaded FileMaker 11.0v4? (There is no 10.0v4 as far as I know.)
This upgrade should not affect your ability to open the file with a password. Are you sure that you are using correct capitalization with your password? (They're case sensitive.)
Do you have an older back up copy of your file? Does it show the same issue when you try to open it?
Yes, I mean 11.0v4.
Yes, I cannot believe it is a mistake with the programme. It must have been my own mistake. As I entered a well-known (to me) password, I must have done it wrong (twice). So my bad. My only gripe with FileMaker is that the characters are not shown when changing the password. If I had seen what I was typing the mistake would have been avoided.
Yes, I have a back-up. So only 6 hours of work lost. C'est la vie!