I have Googled this but don't "get" the advice.
I have Lightroom 5 (Windows 8) and am getting the error message "Folder cannot be found" for many, many images when I try to go to the "development" mode. I upgraded to a newer version of Lightroom a little while ago. I have not been changing the names of theses files. It would appear that something has changed that has affected hundreds of images I have developed. Is there a quick fix to this? Thanks. By-the-way, I am not terribly computer savy.
This message means that your photos or folders have been moved, renamed or deleted outside of Lightroom. On Windows computers, it can also mean your external drive has changed drive letters.
The instructions on how to fix this, with pictures, are here: Adobe Lightroom - Find moved or missing files and folders