thanks chris and gordryd!
yes, it is exactly the RL sample! The camera is in the scene, I double checked the name and it is set to "camera1". In fact, I get the output "camera is available" from the script.
Anyway, I removed the camera and created a new one, leaving its name to the default one ("Camera") and changed the string in FindObject accordingly, and now it works
Btw, do you know where I can see the outputs of "print" commands? They do not show up in the Console log (this is why I had to set a label in the qtwidget to debug...)