I think there is more than one error. HP451dn - on a Mac 10.7
The ipp process on the Mac goes wild and has to be killed.
This could be the communication error mentioned above.
I have turned the printer on and off (yes I did) to fix it. BUt it is definitely hanging and needs a boot to the head.
I found the 49 error as well. I was able to work around that as I could see this printer was having trouble with
landscape oriented pages that were 'auto' changed or something on the Mac. By manually printing them portrait,
they worked fine. I am about to print a bunch of mixed landscape and portrait docs - not expecting that to work.