We can't help you based on that little information: we have no idea even what language your app is written in!
So start with Google, and try the whole error message:
Run time error 3021 - EOF or BOF is true or the current record has been deleted - Google Search[
^]
You'll see that it returns a lot of results - nearly three thousand!
So start looking at them and see what fits your circumstances, then start looking at what they are saying causes the problem.
We can't do any of that for you, but even if it doesn't fix your problem - which it very well might - it will hopefully focus your attention onto the areas you need to start looking at to debug the actual problem.
But we can't do any of that for you!