So many times we have hurdled into this exception when we try and start either the Admin Server or the weblogic instances.
The issue happens mostly when one of the envionment (domain) is copied.
The easy way to fix the same is to re-encrypt the password using the BEA weblogic Encrypt Tool. You can ask your weblogic administrators to do this if you do not have access for the same
java -cp ./weblogic/server/lib/weblogic.jar -Dweblogic.RootDirectory={your domain} weblogic.security.Encrypt {your plain text password}
Also note that once you have this issue, by virtue of it the boot.properties file will have "NULL" for encrypted password.
The boot.properties will be located at
<<Domain_Home>>/servers/AdminServer/security/boot.properties
<<Domain_Home>>/servers/<<Instance Name>>/security/boot.properties
Hope this helps some one struggling.
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