[Android] BitmapFactory DecodeFile ไม่ได้เลยครับ ส่งค่า NULL ตลอดเลย ทำอย่างไรดีครับผม

 public class ImageAdapter extends BaseAdapter 
    {
        private Context context;
        private String[][] lis;
        
        public ImageAdapter(Context c, String[][] li) 
        {
        	// TODO Auto-generated method stub
            context = c;
            lis = li;
        }
 
        public int getCount() {
        	// TODO Auto-generated method stub
            return lis.length;
        }
 
        public Object getItem(int position) {
        	// TODO Auto-generated method stub
            return position;
        }
 
        public long getItemId(int position) {
        	// TODO Auto-generated method stub
            return position;
        }
 
		public View getView(int position, View convertView, ViewGroup parent) {
			// TODO Auto-generated method stub
			
			LayoutInflater inflater = (LayoutInflater) context
					.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
		 
			if (convertView == null) {
				convertView = inflater.inflate(R.layout.layout_listview, null); 
			}
					
			// ColPhoto
			String strPath = "/mnt/sdcard/ProductExpireNotification/"+lis[position][3].toString();
			ImageView imgPhoto = (ImageView) convertView.findViewById(R.id.image_show);
			imgPhoto.setPadding(5, 5, 5, 5);
			Bitmap bm = BitmapFactory.decodeFile(strPath);
			if (bm == null){
				Log.e("ERROR","bm = NULL");
			}
			imgPhoto.setImageBitmap(bm);
			int width=100;
		    int height=100;
		    Bitmap resizedbitmap = Bitmap.createScaledBitmap(BitmapFactory.decodeFile(strPath), width, height, true);
		    imgPhoto.setImageBitmap(resizedbitmap);
			
			// ColName
			TextView txtName = (TextView) convertView.findViewById(R.id.textview_prod_name);
			txtName.setPadding(10, 0, 0, 0);
			txtName.setText(lis[position][1].toString());
			
			// ColAmount
			TextView txtAmount = (TextView) convertView.findViewById(R.id.textview_amount);
			txtAmount.setText(lis[position][5].toString());
		 

			return convertView;
	
		}

    }

Bitmap bm = BitmapFactory.decodeFile(strPath);