Leonardo becomes unknown device once I upload the this program (RF24)

Projects Networking, Protocols, and Devices
1

It becomes unknown device in Windows 7 64bit

The com port to the Arduino disappear in the IDE
And I cannot upload another sketch to recover it..
What happened and what can I do? please help. =( =( =(

#include <SPI.h>
#include "nRF24L01.h"
#include "RF24.h"

RF24 radio(9,10);

const uint64_t pipes[2] = { 
    0xF0F0F0F0AALL, 0xF0F0F0F0BBLL };

void setup(void)
{
    Serial.begin(38400);
    radio.begin();
    radio.setRetries(15,15);
    radio.setPayloadSize(8);
    radio.openWritingPipe(pipes[0]);
    radio.openReadingPipe(1,pipes[1]);
    radio.printDetails();
}

void loop(void)
{
    unsigned long time = millis();
    Serial.print("Now sending %lu...");
    Serial.println(time);
    bool ok = radio.write( &time, sizeof(unsigned long) );

    if (ok)
        Serial.println("ok...");
    else
        Serial.println("failed.\n\r");

    delay(1000);
}
2

Dear all,

I have a little bit luck that, I have a USBasp and I use it to reload the bootloader in the Arduino.
After the bootloader is send to the Arduino, it run the built-in blink example.
The arduino becomes normal again.

But I am not understand the reason of the board become Unknown Device after I upload the attached sketch to it.
:roll_eyes: