Lpc2000

I have made some tests on the Program CheckSum generated by IAR 
compiler and there is realy something fish.

First I edited the segmentation to place the CheckSum as first byte 
after the end of my code:
--------------------------------------------------------------------- 
?CHECKSUM   CHECKSUM          __checksum       00037FFF  
Program     Relative 
module      segment 
            00037FFF - 
            00037FFF
            Segment part 1. 
            ROOT.  
--------------------------------------------------------------------

The IAR compiler informed me the value and calculation range
----------------------------------------------------------------------
Checksums

Symbol      Checksum  Memory  Start      End 
__checksum  0xcc      CODE    00000000 - 00037FFE 

-----------------------------------------------------------------------

I selected the simple checksum (not any CRC) and wrote the code below 
to test it

/*-----------------------------------------------------------------
CheckSum calculation routine
-----------------------------------------------------------------*/
void CalcCheckSum(void)
{
   unsigned char *pby;
   unsigned char *pCksGen;
   unsigned char CksGen;
   char STRCksCalc[] = "AAAAAAAAAAAAAAAAA";
   char STRCksGen[] = "AAAAAAAAAAAAAAAA";

   // Indicate start of the calculation
   UART_PutStringByPolling (UART0, "\n\rCalculation Start.\n\r"); /**/
   UART_PutStringByPolling (UART0, "\n\r\n\r");

   // Point to Address 0x00000000
   pby = (unsigned char *)0x00000000;
   // Start the Sum with zero
   unsigned char ValCheckSum = 0;	
   // Sum all bytes between 0x00000000 and 0x00037FFF.
   for (long byte = 0; byte < 0x00037FFF-0x00000000; byte++) {
     // Read a byte and sum it
     ValCheckSum += *pby;
     // Increment pointer
     pby++;
   }

   // Indicates the end of the calculation
   UART_PutStringByPolling (UART0, "\n\rCalculation End.\n\r"); /**/

   // Get the value of the CheckSum stored in the firmware
   pCksGen = (unsigned char *)0x00037FFF;
   CksGen = *pCksGen;

   // Transform both values in string
   sprintf (STRCksCalc, "%x", ValCheckSum);
   sprintf (STRCksGen, "%x", CksGen);
   // Send the Vavlues by the serial
   UART_PutStringByPolling (UART0, "\n\r\n\r");
   UART_PutStringByPolling(UART0, STRCksCalc);
   UART_PutStringByPolling (UART0, "\n\r\n\r");
   UART_PutStringByPolling(UART0, STRCksGen);
   UART_PutStringByPolling (UART0, "\n\r\n\r");
}

How ever when I runned the code the genarate value and calculated 
values are different:

==============================================================
Calculation Start.

Calculation End.

22 - Calculated
cc - Generated by the compiler
===============================================================

Does any one call tell me what I do wrong or provide me a sample?

Thanks