Pacoo wrote I think the firmware is updated by the ISP. I've heard that TP-Link want something like service ticket number from the ISP people so that they can contact to the ISP to urge them update...

Delete it first and then add it again into the app, here is an FAQ about this issue, hope it helps: http://www.tp-link.com/us/faq-1562.html

Did you try hard reset the bulb? Was your wifi network changed? Your WiFi network should be 2.4GHz, secured with a password of WEP or WPA PSK security type.

Good work, pal

It's a USB printer or wireless pritner?

I don't think you can do that, it doesn't look like it's designed that way