What is the control source of the text box?
"lots of field labels and fieldnames are needed"
This is an indication that your database is not designed properly. Relational databases should be tall and thin, not wide.
Access permits you to store line feeds in a text field so you don't really need multiple fields for the address. You also show multiple date fields which should probably be in a child table.
Edit: Whoops I missed a couple of points that John didn't. John is right that Previous addresses would be in a child table. Whenever you have fieldnames with numbers like your Previous Address fields, that is called a repeating group and violates normalization rules.
I also missed that you were trying to type in the control in Design mode. That's why you can't.