Physical resize option fails

Hello.. me again,

I've been trying to improve the appearance of the pages when they are not zoomed in. Ovviously, if the smaller images are sized to exactly the size of the pages, then they won't appear all pixelated.

There is the option to physically resize the images and I have been testing that. This is what happens when I have the page size set to 450x600:

1. A 6 page PDF is first converted into multiple 25Mb temporary files, one for each page.
    
2. Then, those temp files are each converted into one 600x800 and one 750x1000 pixel jpg image named: vignette_prefixe_image-00.jpg and vignette_prefixe_image-00_Large.jpg
    
3. Then I can see in the folder that an extra image file is created named: vignette_prefixe_image-00tmp.jpg
    
4. When I check the image, it has the correct size after the physical resize: 450x600
    
5. At this point the browser says 1 of 6 pages created... and it stays on that for quite a while.
    
6. Then it pops up the alert "PDF Converted"
    
7. I note that no additonal 450x600 images have been created
    
8. When viewing the book, it either doesn't show anything, or it displays the 600x800 pixel images at full size in the 450x600 pages, which doesn't work either.
    

So, the net result of the above is that the physical resize option is having trouble creating image files.

The Windows Application log shows this:

An unhandled exception occurred and the process was terminated.

Application ID: /LM/W3SVC/14/ROOT

Process ID: 4008

Exception: System.NullReferenceException

Message: Object reference not set to an instance of an object.

StackTrace:    at Aricie.DNN.Services.FileHelper.ResizeImage(Int32 FileId, Int32 Height, Int32 Width, Int32 PortId)
   at ThreadParams.ImportFromFolder(Int32 FolderId, Boolean Overwrite)
   at ThreadParams.ExtractAndMakeIt()
   at ThreadParams.ExecuteThread()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.runTryCode(Object userData)
   at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

What do you think.. is this fixable?
I'm running this on DNN4.9.5 on IIS7 in 32 bit Classic mode in case it matters.

Regards,
Rob