Comment 4 for bug 1815238

This is still occurring as of 3.11, in both Dojo and Angular PO interfaces. It gives the same user-visible-but-unhelpful error message as noted above in XUL, but it doesn't identify the bib(s) in question nor does it offer a path to resolution.

A workaround (ish) is that you can activate without loading copies, which doesn't of course solve the real problem.