Visual C++ :: Internet Explorer Displays Blank Page When Opening Local File While Screen Is Off?

I'm making a small MFC module that should generate a report (formatted using HTML) and then display it for a user on schedule at 8:30 AM every day. Pretty straightforward stuff.

I compose my report and then save it as a local HTML file in the CSIDL_APPDATA folder. I then use the following calls to display it using the default web browser (Internet Explorer in this case):

Code:
//Error checks are omitted for brevity
CoInitializeEx(NULL, COINIT_APARTMENTTHREADED | COINIT_DISABLE_OLE1DDE);
ShellExecute(NULL, NULL, strSaveFileTo, NULL, NULL, SW_SHOWNORMAL);

This module is run on schedule from the Task Scheduler. (The task is set up to run when a user is logged on, which is all the time for that PC. It is never turned off, put to sleep, etc. That computer has only one user that is never logged off either.)

This works perfectly fine when I test it by setting the task a minute or so in the future. But when the actual task is supposed to run at 8:30 AM, when the user wakes the screen all they see is a blank Internet Explorer page. (Note that if someone refreshes that page by hitting F5, only then my report is shown on the screen.)

So I started looking into it:

1) I checked that the file is properly saved (before calling ShellExecute) by reading it back and by comparing it with the original HTML markup that I saved earlier. It's all correct there.

2) I then checked the power saving options. That computer is set up to show screensaver after 5 minutes and to turn off screen after 25 minutes.

3) The web browser that causes this issue is IE version 11, with the latest updates installed. The operating system is Windows 7 Professional.

And why is IE showing a blank page only when computer is running unattended?