already answered very comprehensively here on Fixya!
The Bunn Ultra-2 originally came with several circuit boards, including the main control board and a small memory board also known as the "TIC Clock". This little board, screwed in directly behind the main control board and has a small round metal circuit on it that looks like a watch battery, but it is not -- the metal "Can" contains the timing and memory functions for the main control board.
There is also a small battery inside the "can", which maintains the memory when power is removed from the machine. Over time, this battery will fail and you will see an error message on your LCD readout that says ":Bad TIC Clock". In the past you could just buy a new TIC Board from Bunn and install it and you'd be back on your way again. But, Bunn no longer sells the TIC Board and instead Bunn wants you to purchase a new Main Circuit Board that has the memory and timing functions built right on the new Main Board. The list price is over $200.
You can now purchase a TIC Board Rehabilitation kit from the Margarita Guys for under $50 which will replace the failed circuitry on the small TIC Board. Go to ebay and search "Bunn TIC Board" and you will see the kit available there. It includes all the necessary tools, 9 pages of detailed instructions and annotated photos, free Priority Shipping, and free phone access to their Bunn trained and certified Journeyman Technicians for any help you may need.
This should be the perfect answer to resolve your Bad TIC Clock message and the working errors that come with it.