"not a valid package archive" when trying to install PHP extension?

I'm running CENTOS 6.6 on a VPS and am trying to install the ZMQ PHP extension and tried installing using the command shown in the instructions:

sudo pecl install zmq-beta

However, it fails, showing this as the output:

root@host [/zmq]#  sudo pecl install zmq-beta
downloading zmq-1.1.2.tgz ...
Starting to download zmq-1.1.2.tgz (39,573 bytes)
..........done: 39,573 bytes
could not extract the package.xml file from "/root/tmp/pear/cache/zmq-1.1.2.tgz"
Download of "pecl/zmq" succeeded, but it is not a valid package archive
Error: cannot download "pecl/zmq"
Download failed
install failed

I also tried:

sudo pecl install -Z zmq-beta

And:

sudo pecl install --nocompress zmq-beta

But I get the same error.

Why is this error occuring?