In WebLogic 8.1, if you change the administrator's password from the console, the server will fail to start when you next restart it. The error message is:
<BEA-090402> <Authentication denied: Boot identity not valid; The user name and/or password from the boot identity file (boot.properties) is not valid. The boot identity may have been changed since the boot identity file was created. Please edit and update the boot identity file with the proper values of username and password. The first time the updated boot identity file is used to start the server, these new values are encrypted.>
The solution proposed in the error message works.