The D700 was first supported by Lightroom 2.1 so LR3 should have no issues reading those RAW files.
If you're using Nikon software to transfer the files from camera to computer, try eliminating it. Older versions of Nikon software are known to render Raw files unreadable by Adobe software.
Use a card reader instead or connect the camera direct to the computer.
Hi, I am using a card reader. I have used this software on my desktop with this camera for 3+ years. This is something new from all devices.
"Cannot read file" normally indicates a problem with the permissions on the destination folder.
After you check the Import dialog settings to make sure the destination folder is set as you want, use Finder/Explorer to verify that you have READ and WRITE permissions on the destination folder and its parent folder.