I recently noticed that whenever I attempt to engage someone in a private conversation I uncharacteristically never get a response. So I clicked on the heading for the chatroom name and see this message:

(user handle) Target change too fast. Please wait 29 (or other number) seconds.

What does that mean? How can I have a conversation?

It means that you tried to do too many things at the same time. An example of this (but NOT limited to this one example) is if you try to mass ping a channel and send a noticwe to them what their ping time is..... after a certain number of notices the network cuts you off so you dont flood and gives you that type of message