"File does not exist" usually indicates that while LR has a preview of the image (which is what you see in the LIbrary Module), the original image file is not available. It could be that the original is in a folder that has been moved or it's on an external hard drive. In your case, it may mean that when you were importing, you chose "Add" instead of "Copy".
- "Add" leaves the image in place (or your card) but adds a preview and metadata to the LR catalogue;
- "Copy" does the same as above while, at the same time, copying of the image file to whatever folder you have specified in the Destination palette in Import (right side)
This has been an ongoing difficulty with users of LR - that is understanding exactly what is happening during import - Copying versus Adding - and has led to images being erased from memory cards without them actually being uploaded.
When looking at the images in the Library Module, do you see a small icon in the upper right with a question mark?
If so, it means the original file is not available. Upon Export, you would get the Error Message that "original file could not be found".
Clicking the Question Mark icon will bring up a dialogue "xxx could not be used because the original file could not be found. Would you like to locate it" and it provides the last known location. Try navigating to that location and click on the file. If that last known location is your memory card, hopefully the file is still there and you can perform a proper Import using "Copy". Otherwise your photos may be gone for good, unless you can recover them from the memory card using a recovery application.
I hope this helps and that it turns out well for you.
