Is there a way of deleting a particular preview if I don't want it? Maybe this is related to the same question: When I click on one of the preview images, a cross and other symbols appear on it. I can't seem to figure out the function of these, can anyone explain them please?

Also, several of my paid for items are grey in my Collection. Some are not completely downloaded and seem to have stopped downloading. One of them has not started downloading, and when I hover the mouse over it only a cross appears. What do I need to do to get this one to download?