Sorry, I always forget some bit of information. I'm using Archive.
I'm sorting new comics into my collection, so I'm changing the value in my item custom field of "Storage Box" for items shifting to a new box. I've done this every month for years without trouble.
For example: I did a Find search for items in Storage Box "8." I selected the comics that were shifting to a new box, hit Ctrl+G like always, and I got the error message.
However, when I got out of Find and just went to a regular title page, like Fantastic Four, I selected one item, hit Ctrl+G, things worked perfectly. I selected multiple items on that page, hit Ctrl+G, things worked perfectly.
So I ran the Find results again, but single selection or multiple selection, I still get the error, so it's only a problem when I'm trying to do a change on the results of a Find search.
I hope that makes sense. I feel like I often try to explain things and fail to make anything clearer.