I use Harman FB Matte quite often. My 4880 makes great prints on it using a profile generated with EyeOne software. So I am sure the system works well.
Still not enough details from you, but make sure of the following: Print dialog is set to PS manage colors, your Harman Gloss profile is picked and printer management is turned off.
Do other papers work for you? Have you run a nozzle check?
What paper do you choose in printer dialog when printing on Harman?