I’ve had to deal with cryptic “PCL XL” errors at work and they have been a bugger to track down - intermittent, non-duplicable, etc.
That said, try a PostScript driver for your LJ2550, that will probably fix it (download from HPs website). It’s also much better at handling PDFs which depending on your line of work can be a large chunk of the print jobs.
Oh, and how old is the PCL6 driver that you are using? If it’s getting long in the tooth, download the latest from HP.
Updating the driver would probably do it as has already been said. If all else fails you can also try the Universal Print Driver from HP that I wouldn’t normally recommend, but it would be worth a shot if you’re getting desperate.