Same here. I have been having a lot of problems with hackers inserting hidden links (display:none) into my posts so I’ve decided to rename the tables. After doing that I got the same error message.
Now looking at my sidebar configuration I find they are all empty. I can create new widgets and that fixes the error message but the old widget set up is gone.
I’m going to see if I can find this information in my backup and restore the necessary entries.