The images that you see in Library Module says " Photo is missing " , is because the images have been moved from their actual location.
Please click on the exclamation mark on the top right of the image and then locate the missing image from the finder.
Please let us know if it helps.
Thanks for the suggestion, Tanuj, however it is not in the File section of the Library Module that I have the problem, there all the images are present and can be edited. It is when I go to my Collections and try to open an image from one of my Collections that I get the message that the file is missing. I get the message for all my Collections. On the left hand side the various Collections are not grayed out and I can see the thumbnails when I open a Collection however the histogram is missing and just below where the histogram is usually displayed it says "file is missing". There is no exclamation point anywhere in the thumbnail or anywhere else.