edition impossible

I have a problem with Amaya.
After a lot of hesitations I decided ti use it, but some html files are
not editable.
I don't understand why : I created an index.html file which I can edit
and modify.
Now I have created severall pages based on the same model (I used the
save as command) and this files are not writable : I can open them, but
I can't type anything !!!
What's the matter ?

Thank you