The simple -- but unfortunate -- answer is that the plugin doesn't work at the moment; it contains some broken role import code. I've filed this at http://pkp.sfu.ca:8086/bugzilla/show_bug.cgi?id=8463
for attention and will treat it as a priority.
If you'd like to work around this in the meantime, you'll most likely be able to do so by:
- Using the user import plugin, with no roles specified, to import the user accounts themselves
- Run a couple of DB queries to associate them with the user roles you want to grant them
This is especially true of you only want to import a single role. I can help with the SQL part of this.
Public Knowledge Project Team