Interrupt is not working

Hi

        I am working with AM1808 experimenters kit. I am trying to use port interrupt gp4[14]. The GPIO configurations are shown below.

        #define GPIO78_PIN  GPIO_TO_PIN(4, 14)

       In interrupt __init  The fallowing configurations are made.

        gpio_request(GPIO78_PIN,"interswitch");
        gpio_direction_input(GPIO78_PIN);
        gpio_get_value(GPIO78_PIN);

        set_irq_type(irq_num, IRQ_TYPE_EDGE_FALLING);
        irq_num = gpio_to_irq(GPIO78_PIN);
       if (request_irq(irq_num,interrupt_handler,SA_INTERRUPT, "interrupt", NULL))
        {
                printk(KERN_ERR " Cannot allocate the IRQ(%d)\n",49);
                return 1;
        }

In the above code in interrupt module is geting compiled. when i am trying to do insmod, module is geting inserted but it is throwing the error  Cannot allocate the IRQ(49). Can you suggest the way how can i solve this problem.

Thanks

Vasu Vallabhaneni