Text widget "Show widget on " option ??

I have a text widget that I want to be displayed on one single page.
In the widget there are these options All pages / Selected pages / All pages except selected.
The second option should do it, I suppose, but regardless of what I write in the page-id selection box, it keep showing the widget on all pages.
Finding the page-id is not obvious. It is not visible anywhare on the page editing page. But I use the number displayed with the Short link button at the top of the page ( maybe the problem is that I am using the All in One SEO Pack plugin???)
How can I show my text widgets on just a single page?

I know that there are plugins that can do it, but I don’t want them. I had everything running on my page until I updated WP yesterday and it simply erased the plugin AND all my textboxes including content without even warning me!