"Bitmap is not valid" error

Hello everyone.  We are having a problem that seems to show up on Windows
NT.  I am posting this on a couple of the different Delphi groups since it
may or may not be a "graphics" problem.

This is a simplified snippet of code that I am using in a DLL. This
procedure is called at least once a day. The main purpose of this is to show
a progress indicator of where we are at in the process. I have a feeling
that this is related to memory, but once the main process calls this DLL, it
continues to process without any problems so I am not sure what may be
causing it.

The form contains 15 TImages. These are used to indicate what is turned on
and what is turned off. Depending on this information I have 2 invisible
TImages that contain glyphs. 1 is called imageX and the other is called
imageCheck. If the feature is turned on I replace the picture of 1 of the 15
TImages with the picture of imageCheck.  If the feature is turned off I
replace the picture of 1 of the 15 TImages with the picture of imageX. I
know it is crashing on the create of the form, because once the form is
successfully created I write something to a log file indicating this. The
output to the log file is never written. Here is the code I am using and the
error that is returning.

    formProgress := TformProgress.Create(Application);
      {-write something to a log file}
      {-do processes}
    on E:Exception do
      MessageDlg('Unable to create report for today!', mtError, [mbOK], 0);

The error this reports is:

Unable to create overflow report for today!
Error reading imageX.Picture.Data: Bitmap image is not valid

Does anyone have any ideas.  We are having another problem with this
application that makes the screen turn "gray" and components start
disappearing off of the main form, as well as from other windows.  
Eventually you can't do anything since everything has "disappeared".  If you
click on an area of the screen, you can briefly see that "area" as Windows
redraws it, but it is soon gone again.

We suspect some type of resource leak (is there some type of Video resource
leak that could cause this?)  We have check it with Memproof and Memory
Sleuth but couldn't find anything.  We have also run the System Resource
monitor under NT as well as the Task Manager monitor and have found nothing.

Has anyone out there experienced anything similar to this?

Thanks for any help.