LPC1788 USB HOST HID

I want to add a usb keyboard to my LPC1788 board.
I'm using RL-USB for it. I have successfully used RL-usb to read and write a usb flash-drive.
But i can not get it to work with a usb keyboard, usbh_hid_status(0, 0) always returns 0.
anybody knows why?

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