I need to read this more in-depth.
Suppose it is easy to send messages to the past, but that forward causality also holds (i.e. past events determine the future). In one way of reasoning about it, a message sent to the past will "alter" the entire history following its receipt, including the event that sent it, and thus the message itself. Thus altered, the message will change the past in a different way, and so on, until some "equilibrium" is reached—the simplest being the situation where no message at all is sent.
Chronotech assumes that the simplest version still has a message being sent, but other than that this is a fair description of how it works.