Nirsoft makes a program SysExporter that can extract the contents of most windows, in the windows systems.
I like to call it a Window snagger, it can grab text of just about anything. titles, status, text boxes, context menus even html off a web browser.
Because it is getting the contents from the system itself , even hidden items will be able to be seen or extracted. You could use it in this situation to see all the text that belonged in that text box.
Once it is running just drag that target circle to the exact location you want to grab.
Tips from using it:
You may have to Run_As Administrator.
It helps to have other stuff
closed, and minimal things going on in other windows generally, it
will even lock-up (not responding) on my machine with too many things
going on and being updated.
Without sounding like an ad, tools like this can come in handy for
many other purposes, a good one to have in your utility closet :-)