Well Kgallen you have saved the day. After all I only had to read the f.manual.
I was doing it all wrong. I was trying to assign a fixture from the floppy containing a cft file and the mixer didn’t recognize it.
I did what you said, loaded the cft file and replaced the existing one in the desk. After that I tried to assign a fixture again and there it was, the cft file I previously loaded.
I thought we could just add one more fixture to the file already existing in the mixer. But you have to create a new file and replace the existing one. I have now, in the mixer, a fixture file containing only...one fixture!
It was, also, only after reading the manual, I realized I had to reboot the mixer to implement the changes.
thank all you guys again