Sorry that you cannot import images from SD card into Lightroom using the "Add Photos" option.
Which version of Lightroom are you using and on which operating system? Are you able to import from your local drive otherwise?
Would you mind resetting the Lightroom app preferences to default? Press and hold the Shift + Option + Delete keys.(Mac) or Press and hold the Shift + Alt keys while starting Lightroom. A dialog box should appear asking you restore the preferences.