How to set the block library slide file:

First use the PLANBLKS or ELEVBLKS command and navigate to the menu that you would like to customize (the one that is not showing the correct background image).

Then select the button at the bottom of the menu. When this button is pressed the current menu changes to the "Customize" menu and is divided into it's 40 cells like shown here:

If you are in one of the menus that has already been set up for you and would like to use the "standard" slide file for the menu check the "Use default slide" box. The correct slide for the menu will be shown. This applies only to the menus that come set up when you install the APS software for the first time. Any other menus must have a slide file defined for them, see below.

For the menus that came set up with the APS software, if you would like to show a background slide other than the "standard" one, UNcheck the "Use default slide" box and "Browse..." for the slide file that you would like to use. For all other menus since there is no "default slide" you must "Browse..." and locate the slide file that you have made for the background for this menu.

I tried this and it still doesn't work.