I've seen numerous postings on this issue and even a couple that say "Solved!", but it is not so.
I have an existing report that is up-to-date and good to go, but I have several dashboard tiles that are built from this report that haven't updated to reflect the change in the data. I've tried a few different solutions, closing down my browser / logging out, etc. but they haven't helped.
This error also appears on the dashboard app on the iPad as well.
Very frustrating.