Dear Nick,
the author of this extension use an experimental installer that they have created and that cause problem to be installed under JMS automatically.
You can have a look in their website and they publish themselve an alternate procedure to install their component.
You can also have a look in a reply I have given for another extension published by this company.
See forum
www.jms2win.com/forum?func=view&id=582&catid=3
The problem with this author is that they have developed a fake component called "com_nonumber-installer-UNINSTALLME" that is used to install the component itself.
When the component is installed, they delete this "temporary" component but in Joomla they keep the name of this temporary extension.
Therefore when JMS want to re-install the extension in a slave site, it retreive from Joomla the name of the temporary extension that they have deleted.
This explain why you have to unzip this extension in to a directory of the Joomla administration to restore this temporary installer.
This will allow JMS retreive its version number and previous installation and will allow the re-install in the slave site.