How to write NVM flash?

Question

Hi,
I use the nrf24le1 device in my design. I want to stroe data when power is off, so I write data to the NVM flash. But something is wrong in my design, could you help me ?
I have two codes, the first code is described as follows:
The flash is earsed firstly, and then I write data to flash, the address is set to 0XFB80, then I read the data in flash, the data which is read is correct.
After the first code, I program the second code to the device,the second is described as follows:
I read the flash directly, and the data which is read is FF.
In my opinion, I have writen the data to the NVM flash sucessfully, the data would not miss when power off. In the second code, I don't write the data to flash, I should read out the data which is writen in first code, but the result is failed. what's wrong with my design. 
 static xdata uint8_t AES_Key[16] = {0xcc,0x77,0x44,0x18,0x87,0x56,0xb3,0x7d,0x99,0x10,0xc7,0xcc,0x13,0x14,0x15,0x16}; 
 uint8_t data1_buf[16];
void main(void)
{
uint16_t addr;
uint8_t i; 
 mcu_init(); 
 EA = 1; // Global interrupt enable 
 hal_uart_init(UART_BAUD_38K4); 
 addr=0xFB80; // set the flash address 
 while(1) 
 { 
 if (!S2)
{ 
 //hal_flash_page_erase(33); // In first code 
 LED=0; 
 //hal_flash_bytes_write(addr,AES_Key,16); // in first code 
 hal_flash_bytes_read(addr,&data1_buf, 16);
for(i=0;i<16;i++)
{
hal_uart_putchar(data1_buf[i]);
}
LED=1;
delay_10ms(); 
 } 
 } 
 }