Hi, I find a simple bug that causes an error message on activation although it doesn't affect the operation of the plugin. The bug is on line 641 of co-authors.php. Here is what is says:
register_activation_hook( __FILE__, array(&$edit_flow, 'activate_plugin'));
Here is what is should say:
register_activation_hook( __FILE__, array(&$coauthors_plus, 'activate_plugin'));
Obviously this is a copy/paste error from the EditFlow plugin code. It doesn't have an affect because while Co-Authors Plus has an activation function it doesn't do anything, but the error message leads to the user wondering if it there was any problem.
Please acknowledge this bug report so that I know you'll make the fix.
Hope this helps.