I found this solution once before, but for the life of me can't now. In photoshop, while editing, my images are of the correct resolution. But when I save them they are squeezed on the left and right. I know this is because the "scaled" feature is enabled in photoshop. How do you turn this off?
This is just a guess but since you are editing a YouTube video frame, the pixels are not square and PS has automatically set a non-square viewing mode. This is useful if the frame you are editing will be going back into the video, but not useful if you want to save it as a still image.
There are several Pixel Aspect Ratio options on the View menu.
Here is someone with the same question in 2005:
Oops! You put the link from this question in your reply =)