Thanks for taking the time to reply. The problem is now solved, as explained below.

However, what you said was “impossible” apparently is possible. I eliminated the two points you mentioned as follows:
1. I logged off and back in again at least twenty times. Every time the password worked. Then I ...

I think I have read the Start-Up Guide and searched the Wiki thoroughly, but there is one basic thing I still can't seem to get right. I can't run sudo commands in terminal and I can't run applications in the System category that require a password. Permission is denied.

So far I have only created ...