If you're changing your FileVault-enabled password, change it only from the Accounts preference pane.
If you’re using FileVault and you need to change the password, be sure to change it from the Accounts preference pane as that will update the keychain as well. This may seem obvious, but I ran into a problem where somebody had changed the password to a server’s FileVault-equipped admin account by some other means (probably Workgroup Manager.) The result is that I could not log into that account from the login screen. It’d take the password (since NetInfo said it was right), and then hang since the password to unlock the the FileVault sparseimage was different. The only way to get back to the login screen was to look up the loginwindow console process then kill it via SSH. I wound up having to create a new admin account and blow away the old account since nobody could think of what password the sparseimage might be using.
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Don’t let this happen to you; always change your FileVault-equipped account from the Accounts preference pane!
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