Faulty cartridge error

[D Hook]

Have you gotten a chance to download the service manual?  I just took a look and, I may be mistaken but it shows your printer taking a 773A.  Take a look at page 79 in chapter 3 and it shows the numbers of the cartridges for you model.

I had a co-worker that had the same printer as yours and after his introductory cartridges ran out he ordered a set of new cartridges as listed in the owners manual and found out HP had changed the number without anyone knowing so none of his new cartridges worked.  You might be encountering the same problem but I'm not able to access information to be absolutely certain this is the case here.  It might be a question posed directly to HP or one of their techs or where ever you purchased the printer.

*EDIT*  The caveat to this is that if you put in the old cartridge that DID work at one time, but now does not, it might point to some other problem like the sensor in the ink supply station not making contact with the cartridge.  Sometimes reinserting and wiggling around the cartridge will make a connection but might not stay connected.  Had that happen before.  I could make the cartridge make contact and it worked as long as I kept my hand on it.  Had to make some adjustment to the sensor on the back of the ink station.  Also, a firmware update might have something to do with it.  I take it that when you remove other ink cartridges and reinsert them, they are recognized, correct?  And they're the same 771A like the magenta you're trying to replace?

A quick check on ebay shows both the 771A and the 773A for the same model printer.  If it was my printer, I'd buy the cheapest 773A from Ebay and try it.  This is why I say a conversation with HP might be needed to sort this out for you.  They'll probably want your serial number and your firmware version.  

Or maybe an HP tech/moderator here on the board might be able to help a little more and at least answer the question about the difference between the two cartridges.