Every now and then instead of getting the proper output we get numerous pages, mostly with just a single line, of output which appears to be the raw PCL. My theory is that this happens when the first byte or two of the document is somehow not received by the printer, which then doesn't know how to interpret the rest and does it's best by spitting it out as text.

This is a problem I've seen many times over the years but has been popping up more often since we upgraded to Win 7 64 bit, which introduced a number of headaches because of the HP lack of real support for 64 bits. It also appears to happen most often when printing PDF files. We have tried several different PDF readers in addition to Adobe's own but that hasn't helped.

While we mainly use HP printers, and the problem is not limited to any particular model, I've also seen it happen on other brands, albeit to a lesser extent. I've also been unable to discern a difference between printers used via a print server or those connected directly by IP address. It also happens to USB attached printers.

Because of the erratic nature of this problem there is precious little I can think of to try and debug it, so I'm after any ideas that might help to eliminate it.