After taking photos and importing them for the first time Lightroom will sometimes decide that a portion of the photos are already in the catalog. I need these photos in Lightroom, but it refuses to let me import them. I have tried unclicking the duplicate box and force ejecting the card, different cards, new cards, importing straight from the card, either by selecting it in lightroom or dragging from the card, no luck. PLEASE HELP ME!!!
Occasionally bugs of this type are reported, the suggestiosn I have for you are; Delete your preference file then restart Lightroom, see if the import works now rename the original files somehow, for example, put the letter A after the file name, such as IMG_5461A.CR2
I just encountered and overcame this bug. Here is exactly what I did to fix it, and I can confirm it worked. What follows are instructions for the Apple environment...
1. I opened the original files in Finder, and confirmed their location
2. I batch renamed the files using Adobe Bridge (open Bridge; in the Folders section, locate the folder with your pictures; ensure the pictures are shown in the Content section, then click Workflow, create a new Batch Rename workflow, add a sequence number).
3. The copied files are then found in a new subfolder of the original locations, called Workflow.
4. Inside Lightroom Library, click import, and reimport the files in the Workflow folder into your Library.
5. Finally, I located the partial folder in my Library and removed it using Control+click > Remove.