You should be able to copy the items to the computer. However how you are connecting to the computer may be the issue.
If you are taking the SD card out of its original device and placing it into the computer, then this may be your issue. Especially if the original device made changes to the card. It is better to leave the SD card in the original device and then connect that device to your computer via USB cord and then access the card that way. You should then be able to access the files.