Hi there bagmobile, Welcome to the Forums:)
I'm sorry to hear about the message on the printer you are seeing to install the photo tray, when it is already installed. I do notice that you have power reset your printer by unplugging it and that did not resolve the error.
I would suggest checking to see if the printer needs a firmware update: Getting the Latest Firmware and Product Updates
If updating the firmware does not resolve the issue, I would then suggest calling HP's Technical Support to see about further options for you. If you are calling within North America, the number is 1-800-474-6836 and for all
other regions, click here: http://www8.hp.com/us/en/contact-hp/ww-contact-us.html
All the best,