I also get this error and realized it after I had bought the Pro version because I did not get this error at first while testing the free version of the plugin.
The error look as follow:
There is another active plugin that is conflicting with Register Plus Redux. The conflicting plugin is creating its own wp_new_user_notification function, this function is used to alter the messages sent out following the creation of a new user. Please refer to radiok.info for help resolving this issue.
Can you fix this as it is really important.
