When something goes wrong with calling lpr from tlclient, we tell the user to look in the log file. But this is all you get there:
2014-04-29T13:42:07: Print error: Error when running 'lpr' command to print file
Not exactly helpful. In my case the problem was a missing default printer, which lpr will tell you:
[luser@localhost ~]$ lpr
lpr: Error - no default destination available.
So we really should log the output from lpr, at the very least on errors.