I have installed BEA Weblogic 8.1 on my machine. I used Configuration Wizard to initially create a new Weblogic Configuration. During the process, I gave a username and password. After that I was able to login to administration console using the username and password i supplied during the configuration.
Again, I used "Extend an existing Weblogic Configuration" to add support for JDBC and Datasources. Now I am not able to login to admin console using my username and password. The default weblogic/weblogic is working.
Even i have seen this issue...as a workaround...while extending the domain through config wizard you can see an option "Do you want to configure application security".Here you can add a user(give your username and password) and assign him admin role so that you can login using this credentials.
Also if the username and password is weblogic/weblogic for a domain , and if you extend this domain , you will be successfull in logging to console with this credentials.
If you have accidentally changed the password and don't remember it, here is a workaround.
Search for Boot.properties. You will find the entry for username and password. Remove the values for each of them.
It should now look like
Now when you start the server, it will ask for the user name and password again.