From the FAQ portion of the Hunten web site:
2. My trail camera will not take images. It reads "Full". First, make sure the SD card is not locked. There is a sliding lock on the side of most SD cards. Slide it to the unlocked position. If this does not fix the problem you will need to reformat your SD card. Simply insert the SD card into a computer and right click on the SD Card icon. A drop down menu will be displayed. From here select "Format". A new window will be displayed, click once on "OK". This will promt you to make sure you want to delete everything on the card and reformat it. Select "Yes". Your computer will then begin to reformat the SD card. Once finished, it should work with the trail camera flawlessly.