When you print a test page from the general tab of the printer properties dialogue, it completely bypasses the print spooler. Since your test pages print correctly, this tells us quite a bit. Some of it good and some of it bad.
The printers, base driver install, connections and protocols are all functioning correctly.
The printers, base driver install, connections and protocols are all functioning correctly making it much more difficult to pinpoint the problem.
JetDirect printing through the print spooler can be trouble prone with no clear solution. The fact that the 2600n is a host based GDI printer can make it even more so however I still have a couple of things to try.
1-Search for Localspl.dll and check the version number, file size etc. etc. If it is anything other than:
(32 bit x86)
Localspl.dll 5.2.3790.4046 342,016 23-Mar-2007 20:24 x86
(64 bit x64)
Localspl.dll 5.2.3790.4046 750,080 23-Mar-2007 22:15 x64
then request a copy of this file from Microsoft here:
See KB934885 http://support.microsoft.com/kb/934885
for more info. You may want to try the registry tweak there to see if it can help pinpoint the problem as well.
2-Download the latest firmware for the 2600n from HP. There have been at least 2 firmware updates that I know of for this printer. I don't know if any of the updates fixed issues with network printing but at this point it can't hurt.