What does modification not allowed, selection locked mean?

[Jason M.]

I don't know what happened but I cannot even put a space in between letters
without a message appearing right where it tells you how many words you've
typed. It says,"This modification is not allowed because the selection is
locked". I have looked up help in all ways possible and my mother does not
even know what the heck happened or how to fix it. I severely need to figure
this out so that I can finish typing my biology paper. It is a big part of my
grade and I
absolutely cannot get a bad grade, that would suck. So please, if anybody
has an answer, I could really use it. Thanks for reading this and don't worry
if nobody has an answer, I'll figure it out eventually.

 

[Stefan Blom]

The message might indicate an expired trial version (buy a full version) or
a copy of Word that hasn't been activated (active it). In either of these
cases, the message would appear no matter which document is open in Word.

On the other hand, if you see the message with a particular document, only,
the reason might be that your selection includes a content control that
cannot be deleted (clear the "Content control cannot be deleted" option in
the Content Control Properties dialog box).