Recover your files
You have an "SD error" on the GoPro, you have accidentally deleted some important files or your SD card is simply unreadable ? There is a powerful solution for you : Test Disk.
This little utility can be downloaded here : http://www.cgsecurity.org/wiki/TestDisk
And they also provide a complete documentation here : http://www.cgsecurity.org/wiki/TestDisk_Step_By_Step