Whenever I try to publish a page after applying a Target Activity, Failed to retrieve references for selected pages error pops up on screen. This only happens when we have references applied to a page.
I'm sure you must have fixed this by now but answering so that others can fix this.
I had been facing this problem whenever I was trying to publish a page along with a NullPointerException in the logs . On further digging, I found that AEM tries to find references for the page, including the configurations inside /etc/cloudservices (and I'm sure there could be more).
In my case, a jcr:content node was missing under one of the configurations which was leading to the NPE and the "Failed to retrieve references.." error. I simply copied a jcr:content node from other configs and removed the unnecessary properties, except the sling:resourceType property and was able to fix the error.