Problem Debugging when using Interrupts

Hi
I am using uVision 3 and i have written a source code to enable Timer Counter 0 interrupt in at91sam7x256.
My program compiles successfully and debugger starts well until TC0 interrupt occurs. It jumps suddenly to address 0x00000018 and so show me the very famous keil error message:
no execute/read permission
I have tried my projects RAM.ini file memory map in debuuger settings and so on. but the problem is not that the place my code is stored there or the place in memory that debugger starts from.
The problem is that when Interrupt occurs debugger jumps to a memory space that is not address of my interrupt routine.
This is my code:

#include <AT91SAM7X256.H>                        /* #include <lib_AT91SAM7X256.h>



#define AIC_SVR_TC0IP           AT91C_AIC_PRIOR_HIGHEST

void mainTimer_isr () __irq{

        timer++;

        AT91F_AIC_AcknowledgeIt(AT91C_BASE_AIC);

}



int main (void) {
        // Enable the Clock of the PIO

        AT91F_PMC_EnablePeriphClock(AT91C_BASE_PMC, 1 << AT91C_ID_PIOA);

        AT91F_PMC_EnablePeriphClock(AT91C_BASE_PMC, 1 << AT91C_ID_PIOB);

        AT91F_PMC_EnablePeriphClock(AT91C_BASE_PMC, 1 << AT91C_ID_TC0);



    //* Disable the interrupt on the interrupt controller

    AT91C_BASE_AIC->AIC_IDCR = 0x1 << AT91C_ID_TC0 ;

    //* Save the interrupt handler routine pointer and the interrupt priority

    AT91C_BASE_AIC->AIC_SVR[AT91C_ID_TC0] = (unsigned int) mainTimer_isr ;
/*This address stored well in SVR register.
 the address is like 0x001000840 but debugger didn't jumped to it.
 It jumps to address 0x00000018 all the time:(
*/

    //* Store the Source Mode Register

    AT91C_BASE_AIC->AIC_SMR[AT91C_ID_TC0] = AT91C_AIC_SRCTYPE_HIGH_LEVEL | AIC_SVR_TC0IP  ;

    //* Clear the interrupt on the interrupt controller

    AT91C_BASE_AIC->AIC_ICCR = 0x1 << AT91C_ID_TC0 ;

        AT91F_AIC_EnableIt(AT91C_BASE_AIC,AT91C_ID_TC0);



        AT91C_BASE_TCB->TCB_BCR=0;



        AT91C_BASE_TC0->TC_CMR=AT91C_TC_CLKS_TIMER_DIV1_CLOCK|AT91C_TC_WAVE;

        AT91C_BASE_TC0->TC_CCR=5;

        AT91C_BASE_TC0->TC_IER=AT91C_TC_CPAS;

        AT91C_BASE_TC0->TC_RA=0x002C;

}

Do you know why debugger jumps to 0x00000018 like this?
How could I solve that?
Thanks a lot.