When I connected a newbie LPC11u68 to USB port,it recognized in windows as an USB mass storage device.When I programmed LPCOPEN HID example by Flash magic to it,after resetting the board,my PC can't recognized it.Only when I pulled down PIO0_1(ISP selection pin)it still recognized as a Mass storage device.???
EDIT:
with adding a 470r resistor to the USB_DP line ,all problems were vanished and MCU correctly recognized by PC as a HID device.