lpr not working - scheduler not responding

The Arch Bugtracker knows about this bug/regression which is introduced in the 1.6 cups version:

The default IPP version for requests is now 2.0 (STR #3929)

And most likely your cups server has an older cups version which still defaults to the older IPP version. The workaround from the ARCH wiki:

Using a CUPS 1.6.x client with a <= 1.5.x server

As of CUPS version 1.6, the client defaults to IPP 2.0. If the server uses CUPS <= 1.5 / IPP <= 1.1, the client doesn't downgrade the protocol automatically and thus can't communicate with the server. A workaround (undocumented as of 2013-05-07, but see this bug report) is to put the following in /etc/cups/client.conf:

ServerName HOSTNAME-OR-IP-ADDRESS[:PORT]/version=1.1

I know this is an old thread, but I came across a similar problem:

root@LabelMaker:/home/funvalley/label_maker# lp merged.pdf
lp: Error - scheduler not responding.
root@LabelMaker:/home/funvalley/label_maker# lpstat -t
scheduler is not running
no system default destination
lpstat: Bad file descriptor
lpstat: Bad file descriptor
lpstat: Bad file descriptor
lpstat: Bad file descriptor
lpstat: Bad file descriptor

I found that it complaining that it didn't have a default printer destination.

To give it a default destination I went into cups(http://localhost:631), manage printers, clicked the printer that I wanted be the default, clicked the administrator dropdown, and set to the system default.