When you want to create a Newsletter please take these measures to accomplish just that.
You can go to Connect > Newsletters > View Newsletters -> Find that Newsletter you want to edit > Then Launch it in Builder > Bring necessary changes and save & Exit.
Alternatively you can always copy an existing Newsletter and edit while retaining a copy of the original. Just take these steps to do simply that.
Connect > Newsletters > View Newsletters. Find the last newsletter you sent (with this similar message) and then make a copy of it (button on the menu). You can then launch it in the builder and edit/type the text in.