The first error message seems to indicate that DotImage doesn't recognize the file format. Neither image seems to indicate that the image is too large. I would expect an out of memory error in that case.
DotImage does have an image size limit of about 500Mb or so depending on how fragmented the memory in the process heap is. We do not have a 64-bit version of DotImage, so I would not expect there to be much of a difference using a 64-bit architecture.
What type of images are these? If it's a TIFF, could you show us what's in the header?
Bill Bither
Atalasoft