I am not sure this is your problem but it is worth looking into for the amount of time it takes.
Win stores an image to a location of your choice. Say drive H:\. It will then make a directory with the computer name in my case it would be H:\HomeII. Check that directory for security settings and give your self (The account you are using) full privleges. See if that fixes it.
One other thing If you have previously created an image that directory exists and if you are succesful it will write over it. If you wish to save that image rename the directory and Win will create a new one. Then you will have more that one image.