"This report can no longer be edited or run. Your administrator has disabled all reports for the custom object, or its relationships have changed."
This is really a dreaded error message, if you happened to do something like changing a lookup field to master-detail on an object, then try to use reports associated with it. A tough spot to be in. I was quite confused though, when I saw it yesterday when trying to construct a dashboard. After thinking long and hard and concluding that I'd not committed no such offenses, I set out to find the cause.
The dashboard component was based on a new custom object, which will be the target for snapshots. Nothing special there. No lookup or master-detail fields on it. The object had been deployed, and I can view the underlying report just fine. Well, there's one thing I'd forgotten, it turned out: the dashboard is a dynamic one. And the new object has been opened up to any profile. That means no one can really see that dashboard component other than folks who can "view all". That's not good in production of course... but I'm not quite there yet. The thing has to be reviewed by admins first before opened up to anyone.
Looks like I need to at least allow access to the object by at least one profile explicitly before I can do anything about it in dashboards.
Next time I'd like a more accurate error message please. Well, I guess that's everybody's wish for all kinds of situations...