Media library and permalinks

Hi, can any one help me with the following in word press “Edit Media” permalinks. On some of my images I will get this-:Permalink: http://www.feedinternational.org/shop/ladies/ladies-t-shirt-small-red-cross/ladies-t-shirt…ed-cross-white/ ” ‎Edit” “View Attachment Page” “Get Shortlink” if I click on view attachment page it opens up a 404 error page, and yet some other pages will have-: Permalink: http://www.feedinternational.org/?attachment_id=2643 “View Attachment Page” “Get Shortlink”, when I click on “View Attachment Page” it takes me to the link page with the image on it and no error. Can anyone tell me which one is right and why I have the difference in the permalinks? I have run these two side by side through my settings and I cannot find any difference between the two that I can see I feel that I must be doing something wrong, and can you tell me how to implement the changes that are necessary. I have clicked on the “unattached” link that takes me to a small scroll window with options of what to link to, can any one tell me how this works and the benefits of this? I know this is a bit long winded but I don’t know how else to explain it.
Regards
Brian