I spent about 30 minutes with Microsoft. Their technician looked at my computer by remote access. My computer is on a network, and the Microsoft tech couldn't do a System Restore to an earlier point without permission from my IT people. I will need to see if my University has a contract with Microsoft Professional in order to be able to pay for Microsoft (~$250) to move further in solving this problem. It's the strangest thing. If I save one of my original images (8.47Mb, black+white) as a bitmap in Paint.net or Paint, I can open that image in Paint and save it as a TIFF file. I can save the bitmap image as a TIFF in Paint.net also. If I open an original TIFF image in Paint or Paint.net, and try to save it, even unprocessed, directly as a TIFF image, I get the error messages mentioned above in my first post. This has to be some bug in handling the header of the image files, and I get the bug with either program. In Paint or Paint.net, though, if I first save the original as a bitmap image, then open it in Paint, I can save the bitmap as a TIFF.