My 8500 Wireless says 'replace ink cartridge' but I have done that twice and it will not print.

It's simple, when I replaced the ink cartridge for the printer at it's request, the 940 seemed to be still full.  But I replace it anyway, and the message still says following ink cartridge to resume.  Please help as this printer has been used very little and it should not be giving me this headache.

Thanks