Cannot Single step though code

OK, what silly mistake have I made this time..?

I have just downloaded uVision4. Got a simple bit of code to flash and LED on and off.

However, I cannot single step through the code. When I hit Start/Stop Debug session, all other option get greyed out. .

I seem to have gone through all the project options as well as copying my code to a new project. It looks like my problem is similar to Benjamin's (recently posted). tried all his fixes and still nothing works

Here is my code:

#define at91sam7s256
#include <at91sam7s256.h>


#define LED            (1<<0)   // PA0
#define BUTTON1        (1<<19)  // PA19

static void initialize( void);

int main(void)
{
    volatile long input;
        volatile int n;
    volatile AT91PS_PIO pPIOA = AT91C_BASE_PIOA;

    initialize();

    while(1)
    {
        input = (pPIOA->PIO_PDSR) & BUTTON1;
        input = 0;
        input = BUTTON1;
        if (((pPIOA->PIO_PDSR) & BUTTON1) == BUTTON1)
        {
                        pPIOA->PIO_SODR = LED;
        }
        else
        {
            pPIOA->PIO_CODR = LED;
            input = (pPIOA->PIO_PDSR) & BUTTON1;
        }
    }
}
static void initialize(void)
{
  //Turn on the peripheral clock.  Without this on, inputs do not actually register in the PDSR register
  volatile AT91PS_PMC   pPMC = AT91C_BASE_PMC;          // pointer to PMC data structure
  volatile AT91PS_PIO pPIOA = AT91C_BASE_PIOA;

  pPMC->PMC_PCER = (1<<AT91C_ID_PIOA);                 // enable parallel IO controller clock

  pPIOA->PIO_PER = (LED | BUTTON1);                     // Set PIO to control LED and button.
  // Initialize Input
  pPIOA->PIO_ODR = BUTTON1 ;                            // Disable outputs for INPUT pins. (not needed as all pins default input on reset)
  pPIOA->PIO_PPUER = BUTTON1;                          //Pullup Enable (not needed as all pullups are enabled on reset)

  // Initialize Output
  pPIOA->PIO_OER = LED;                                 // Enable output for LED.
  pPIOA->PIO_SODR = LED;                                // Turn LED off.
  pPIOA->PIO_PPUDR = LED;                               //Pullup disable
}

Please let me know

Thanks