You are trying to put it in space already used for another icon.
Right click the icon on desktop, drag it to the quick launch area, drag it back and forth until you get a place where the circle and diagonal does not show then either "move here" or "copy here".
If no space is available you may have to expand your quick launch area. Move your cursor just to the right of the two >> until you get the two way arrow then left click and drag right until your quick launch area will hold more icons.
It is possible to have hidden icons in the quick launch area. Just click on the >> or expand the area, per above, and they will come into view.
The larger the visible quick launch area the smaller the task bar.
DC
I don't know what I did. The desktop icon in the quick launch has gone to the desktop and I don't know how to move it back to the quick launch. I've tried to drag it there but I get a black circle with a diagonal line through it, and it goes back to the desktop. I have Me. Thank you.

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