I can only import about one-half of my pictures off my Ipad2. I see only half in windows up to a certain date. Any reason why I can only import pictures in a certain date range?

How do I import all my pictures from my iPad? When I try to import pictures into my computer, it only allows to import half of my pictures up to a certain date. I have tried to import using windows and through Photoshop. I can view all the pictures in my iPad 2, but when I go to import it only allows me to import half. I cannot see the other half of the pictures in WIndows. I had already tried restarting both my computer, iTunes, and the iPad. I don't seem to have any problems with my iPhone or other iPad.