Hi, I’m working on a score, after deleting some measures I end up with this red bar that I can’t delete and I don’t know what it is. Do you have an explanation?
THANK YOU very much Romeo
It’s the Insert Mode Stop Position. See here for how to delete it (or scroll up from there to read more about it.)
It’s a sign that your score has been affected by a Hogwarts spell. 
On a more serious note : Pianoléo has just given you the answer. Insert mode implies a beginning and an end. You’ve probably set this end mark without paying attention. 
In case it helps you in future, searching the manual for “red bar” brings up relevant topics about the Insert mode stop position right at the top.