UART PROBLEM ARM lpc1769

I want change easyweb to communicate with the camera and send hex data (camera) up through enthernet computer.
I used the arm to connect to the camera via uart, but my problem is getting data from the camera with a piece of lost data when I put the counter(nn) above 315bytes.
my camera send data HEX about 12kb.
What is my problem?
way to solve?
my code received data from camera: while(1){ pdata[nn] = UARTGetChar(LPC_UART0);

if (nn==280)(break;}

nn++; }