Today I am finding that Lightroom has lost the links to some images in the catalog. That is, I am getting the question mark symbol. However, in the develop module I am not getting the usual message that the file is offline or not where it is supposed to be, but I cannot export these images now. When I try to relink the images, I get a message that that the file is associated with another photo in the catalog. ? All the files and folders are where they should be. This started happening overnight, and I have made no changes to the catalog image storage, unless I did it in my sleep. Also, I have the image files on external drives, and only the images on one of the external drives are affected. I can open the affected images fine in Camera Raw by clicking on them. This is Lightroom 4.4 and I am on a Mac with Mountain Lion. All images are in one catalog, which is on my internal hard drive.