Won't print due to incompatible cartridge?

We understand that your problem is:
I installed a #28 black ink cartridge and a #29 color ink cartridge into my Lexmark 2500 printer/copier/scanner. It keeps giving me the error message that the print cartridges are not compatible with my Lexmark and it refuses to print. These are the same cartridges that I have used for the three years that I have had this machine. What's wrong and how do I fix it?