Printers have a carriage that holds the ink cartridges, the ink cartridges have contacts on them that are connected to internal sensors that react to the fluid level inside the cartridge, those external contacts make contact with the connections on the ink cartridge carriage, this in turn sends signals to the printers internal controller board, it tells it to which level the fluid is inside the cartridge.
If you examine those contacts in some printers, they are merely copper clad pads and can become oxidated causing connection issues.
You can try wiping those contacts with a very mildly abrasive substance to remove this oxidation, try the cartridge again, you'll most likely have to tell the printer you installed a used cartridge for it to register correctly once it has been removed.
There could also be some ink spilled on those contacts as well, I've seen this happen with printers that get a lot of use.
If the problem does not go away with cleaning those contacts, the problem could be with one of the flexible ribbon wires with sends those signals to the controller board, double check those with a VOM meter if you have to.
One probe on the controller board for each ribbon wire and the other on each contact on the carriage, check for continuity and each one.
Edited by MrBruce1959, 03 May 2011 - 12:45 PM.