Problem when adjustment layer is included over an image

Hi, I have a Photoshop CS4. Whenever i include an adjustment layer over an image, Box pops up which shows the usual options such as the color, opacity and mode. However, when another adjustment layer for example, selective color, is added, the options are now different. There is now an option about the media size. Why is this? Can anybody advise me on what to do? Thank you so much.
