XnView Software

I'm using xnview. I think I have found the problem in that the path name of the missing files includes a drive letter which doesn't exist. I keep the images on an external drive and access via USB when needed. Somehow during one session the drive letter got changed. I can change the drive letter via ...

Recently I find that the selection of a category results in a display of little notebook pages. The file names are correct in that the file does belong to the category but I cannot see the file image.
Clearly the link between the category entry and the image file has been lost. Any ideas how to ...