After upgrade, Printer-friendly pages no longer works

Hi. I just upgraded to 5.15, and my printer-friendly pages no longer worked. I thought it was because I needed the latest version of Print, so I then upgraded the module to Print 5.x-4.3 - and still have the same problem.
I don't believe I'm getting any error (I am getting some PHP errors in the logs, but don't think they are related to Print), and the URL is properly configured: http://www.mysite.com/print/4288 (for example) - but Print does not work. That URL simply fetches the home page of my site, i.e., "node."
What could be wrong here? It actually seems to be an issue with either 5.15, or else something on the server - but what? My other modules are working, mostly (except for SimpleFeed, which seems hinky, too - but I think that may be the Feedburner issue). Can I do anything with the code of Print somehow to get this going again? It was working very nicely before the upgrade to 5.15.
Thanks.