LPC2378 crash after interrupt

Yesterday I've opened a thread about a system crash after the execution of an IRQ routine.
After many tests I've isolated the problem and symplified the context in which it happens.

Now the problem I see is the following.

I've only an IRQ routine linked to CPU timer 0. It should be invoked every 1 ms. However after the first call the CPU switches to DATA ABORT mode.

I configure LPC2378 (rev. B) with 72 MHz clock and MAM fully enabled (the problem is present olaso with MAM partially enabled).
The source code is the following

/*************************************************
** INITIALISING FUNCTION
**************************************************/
void ini_base_timer(void){
    PCONP |= (1 << 1); /* power up timer 0 */
    T0TCR = 0;       /* disable timer 0 */
    PCLKSEL0 |= 0x00000004;      /* timer 0 clock = PCLOCK */
    T0IR = 0x11;        /* reset irq flag */
    T0CTCR = 0;
    T0PR = 8;   /* prescaler */
    T0MR0 = 7999;       /* match register 0 */

/* configuration vectored interrupt */
    VICIntEnClr |= (1 << 4);  /* irq disabling */
    VICIntSelect &= ~(1 << 4);/* IRQ interrupt */
    VICVectPriority4 = 8;          /* priority */
    VICVectAddr4 = (UINT32)&irq_base_timer;         /* ISR */
    VICIntEnable |= (1 << 4);/* irq enabling*/

    T0MCR |= 0x03;       /* irq enabling and TC reset on match register 0 value */
    T0TCR = 0x01;       /* start timer */
}   /* end ini_base_timer */


/*************************************************
** IRQ FUNCTION (ISR)
** global variables:
** long sd[32];                     // global array
** unsigned char buffer_rx_fw[512]; // global array
**************************************************/
void __IRQ__ irq_base_timer(void){
        UINT32 cont;

         FIO4SET = 0x01; /* set GPOUTPUT 4.0 */
         T0IR = 1;      /* irq flag reset */

        for(cont = 0; cont < 2; cont++){
            if(sd[31] == cont){
              sd[30]++;
              if(sd[30] == buffer_rx_fw[cont])
                 sd[28]++;
           } /* end if */
        } /* end for */


         FIO4CLR = 0x01; /* clear GPOUTPUT 4.0 */

         VICVectAddr = 0;    /* dummy write */
}   /* end irq_base_timer */

In this condition the problem is deterministic in the sense that every time after the first execution of irq function, CPU switches to DATA ABORT mode (the system crashes!).
If I execute code step-by-step in assembly mode I see that when micro exits from irq function the LR register contains the address of an instruction that causes DATA ABORT exception.
I don't know how a simple IRQ routine can generate such terrible problem!

I'm using GCC compiler (ver. 4.0.3) with optimization level 1.
If I put optimization level to 0 (zero) the system doesn't crash, however the assembly code produced is so redundant to degradate system performance too much!

Have you any suggestions?

Thank you,

Demis