I Googled "Operation could not be completed (error 0x000007a)" and got some hits. Looks like it may be a driver
problem or a print spooler problem. It looks like it was a big problem with windows 7 RC and HP printers. I have an HP all in one on my win 7 x64 PC and haven't got that error message, I'm not trying to share it on the network though. Can't help you with the MAC problem, I don't own one, and have never worked on one.