I'am  a little idiot, but until now, I could modify the code when debugging.

Recently I modified my solution, adding an installation project. I don't
know if I changed some options in project or solution properties during this
adding, but now, if I want to modify code when i debug, I have a message
like this (I translate because I am french) :
'Impossible actually to modifiy thsi text in editor, because it is readonly'
Someone could tell me what to do, to can modify code during debugging.

I appreciate really your help.
Thank you