Thank you, mates! I don’t know what I was doing wrong, but I restarted the machine few times and start from the beginning following a well defined path. I think that other users was replacing the **k file with a infinite time command, so when the file was opened it was impossible to re-overwrite it. Anyway, after few resets everything was working as expected.
I got a shell (user.txt) and with a bit of effort it was possible to get the root.txt. It is such a great machine. Thank you makers. I learned some new tech and very useful stuff about Windows env.
Cheers,