Why are there 2 folders SDCard and SDCard2 on a ViewSonic GTablet?
According to this thread /sdcard is the internal storage of your device. It is so named because Android counts on a FAT/FAT32 filesystem at that mountpoint for data storage. The optional external sdcard mounts to /sdcard2 and is evidently not available via USB from the tablet. These are the "user serviceable" locations in Android. To work with files outside these paths you will need to have root access on the device and use a 3rd party file explorer.