Did you move the images without using Lightroom to do the move?74
This message means that the file was moved/renamed/deleted outside Lightroom and due to that reason Lightroom is no longer able to recognize or read that file.
if you know the location of the original drive on your hard drive, you can relocate that file by following this article : How to find missing photos in Photoshop Lightroom
I did not move the photos. The full library seems to be there, but when I choose 1 and try to develop, I get the file cannot be found message.
There are a number of options available when you choose to import files to your Lightroom Catalog ( Library)
1. Copy / Copy as DNG, this option allows you to copy the original files from their existing location, e.g a folder on an existing drive, internal, external, SD Card from a card reader or in a Camera connected to the computer via a USB port, to a new location of your choice, to a folder of an internal HDD, an external HDD or a network drive of your choice.
2. Move. , this option allows you to move the original files from their location, e.g. a folder on an existing drive, internal or external to a new location of your choice, to a folder of an internal HDD, an external HDD or a network drive of your choice. (the Move option does not allow you to move files from a Card or your Camera.)
3. ADD., this option allows you to add image files to your Catalog from their location, e.g. a folder on an existing drive, internal, external or network drive and the original image files remain at their current location.
The original image file will be located at the location of your choice.
There are no image files in your Catalog File ( or Library) the original files are at the location you choose.
If you choose to ADD files to your catalog from an external drive and then disconnect the drive from your computer, then Lightroom will indicate that the "file cannot be found".