We recently acquired an HP LaserJet P1102w, which has a wireless IP connection. It works fine (Mac OS X 10.8), but from Centos we could not print (using lpd, socket [Port 9100] or ipp), so we downloaded the current version of hplip (3.12.9) and installed it (this was a manual install). No problem there.
hp-check found the printer and indicated a proprietary plug-in was needed, which it downloaded, but then the install failed.
A log at the log [hp-check -t] reveals a number of packages that are "missing/incompatible", such as "cups-ddk", "policykit", "reportlab", "PyXML", etc. (14 total). However, these are not standard packages (in fact Googling them turns up not much). HP was no particular help, suggesting we try a different repository (without suggesting one).

Any thoughts on what is the root cause?

I can post the debug log from hp-check, if anyone thinks that will be of use.

While it would be most interesting to completely solve the problem, we can live with a workaround.

Thanks!

Given the sequence of events you describe, it may be that the "plugin" needs the packages.

I'm not really sure in what sense you mean that searching for the packages on Google did not turn up much, or that they are non-standard packages.

If I google for "Linux PyXML" I get over 63,000 results, and if I restrict the search further to "Linux PyXML CentOs", I still get over 50,000 results.

Looking at a few repositories, I couldn't easily get a good feel what might still be available for CentOS 5.8. But I fairly easily found what I believe are some of the packages for the more recent version of CentOs, 6.3.

AFAIK, PyXML allows programs written in the Python language to interface to an XML parser. So I wouldn't be surprised if the reportlab package that I found for Python is the one that's needed. There's quite a list of mirrors on centos.org, and from there I found a list of some packages for 6.3 here:

http://mirror.anl.gov/pub/centos/6.3/os/i386/Packages/

I realize you are using 5.8, I include the link just to illustrate that it appears some of the packages are on an official CentOS mirror, at least for version 6.3, so some of them seem to be standard/official packages.

In addition, in the third Google result, there was this in the summary:

At least at one time, some of the packages seemed to exist for 5.8 as well. A few repositories I picked at random seemed to have empty package lists for 5.8. But I didn't search any substantial number of repos. So some or all of the packages may still be available for 5.8.

If the pre-built packages are no longer available for 5.8, it may still be possible to get source versions of some of the packages and build them for 5.8, and you are unable to upgrade to 6.3.

HTH.