my interrupt reset!

Hi.
my usart interrupt dont work correctly .when I chek it in the debugger the US_CR value from 0x1A1A chang to the 0x1A1B and after that the usart hang up!!

in other place in debugger when I chek ofter every interrupt the program doese reset! and I dont know why!!

I think hang up is for a lot of reset of program when a lot of interrupt occure.

It's very funny that if I say that if I deletion the

delay_ms(100);

in my program my Interrupt only work one time!
not reset and not anything else!
but only work one time and in secend time the interrupt occure the US_CR from 0x1A1A chang to 0x1A1B
it's mean that the Rx ready bit in US_CR from 0 becom to 1!
OOOK.
pleas Help me .but If dont help me I hang up too!like my micro!

my start up is sam7.s
are you think my problem is that I dont use another start up file .or i must chang it !!!

and thise is my code:

#include "at91sam7x256.h"
#include "lib_at91sam7x256.h"
#include "delay.h"
void Usart0IrqHandler(void);
int kk=70;

int main (void)
{

           volatile AT91PS_USART pUSART0 = AT91C_BASE_US0;
           int rx;
           unsigned int rxok;
           int errorcounter;


        *AT91C_PMC_PCER=0xC0000040;             //Peripheral Clock Enable
        *AT91C_PIOA_ASR=0X0000003;
        *AT91C_PIOA_BSR=0X0000000;
        *AT91C_PIOA_PDR=0x00000003;             //Disable I/O,PA5=RXD0,PA6=TXD0
        *AT91C_US0_IDR =0xFFFFFFFF;                             //ALL OFF USART INTERRUPT DISABLE
        *AT91C_US0_CR=0x000000AC;                               //RESET RX & TX
        *AT91C_US0_BRGR=0x139;                                  //BARD RATE:9600
        *AT91C_US0_TTGR=0x00000100;                         //SET TIME GARD=0

        AT91F_PDC_Open(AT91C_BASE_PDC_US0);
        *AT91C_US0_MR=0X8C0;                             //8bit,No,1Bit Stop,Asaynchron mode
        *AT91C_US0_CR=0x50;                                     //ENABLE RX & ENABLE tx
        *AT91C_US0_IER =0x01;               //rxbufer full interrupt is set
        *AT91C_AIC_IDCR=0x40;                           //DISABLE THE INTERRUOT ON THE INTERRUPT CONTROLLER
     AT91C_AIC_SVR[AT91C_ID_US0] = (unsigned int)Usart0IrqHandler; // Set the USART0 IRQ handler address in AIC
         AT91C_AIC_SMR[AT91C_ID_US0] =(0x00000007);
        *AT91C_AIC_IECR=0x40;
        *AT91C_AIC_FFDR=0XFFFFFFFF;

        while(1){
      *AT91C_US0_CR=0x100;
           rxok=*AT91C_US0_CSR;
           delay_ms(100);
      *AT91C_US0_IER =0x4;
          }
 return 0;
 }
 void Usart0IrqHandler(void){

        int rx;
        int i;
        volatile AT91PS_AIC pAIC = AT91C_BASE_AIC;


        unsigned int rxok;
        int errorcounter;
        errorcounter=0;

        kk=kk+1;
        rxok=*AT91C_US0_CSR;
        if (rxok && 0x1){
         rx=(*AT91C_US0_RHR & 0xff);
         *AT91C_US0_THR=kk;//rx&0xff;
        }


        *AT91C_US0_CR=0x2100;
    *AT91C_US0_IDR =0x4;
         rxok=*AT91C_US0_CSR;


        *AT91C_AIC_EOICR =0x00;   //end point of interrupt



        return;
 }

I set ox00 value in AIC_EOICR registry.It's right or or the problem is for it?
thank's