|Then you have a serious problem.|
The problem is that the file was encrypted, or scrambled, with a certificate that is a part of the account that encrypted it. Without this certificate decryption becomes a very difficult proposition. An account on an different Windows installation with the same name and password is by no means the same account.
Sorry, but unless you have an alternate copy of that file I cannot hold out much hope of recovering it. For important files you really need at least one backup copy.