Errors resizing JPEGs

On my photo upload routine I resize and resample a copy of the photo for the
thumbnail. This had worked for months with 0 problems. Lately, some *.JPG
files have been causing errors with imagecopyresample. But if I take those
files and open and resave in my photo editors (CorelPaint, PhotoShop) they
upload without a problem. Is there an emerging problem with some EXIF data
produced by digital cameras, or am I missing something else entirely?

Thanks