Moving this discussion to the Photoshop Lightroom forum.
The Nikon P7700 appears to be supported since LR 4.2 / ACR 7.2. see the link below.
Why do you say it is not supported.
If you are getting an error message that says that "the files could not be read" that usually you are trying to copy the files to a drive/ folder or sub folder for which you do not have full privileges to "Read and Write". Change this in your operating system.