Could someone tell me why the objects in the database were invalid, it happened three or four times already, I checked with the users and they didn't run anything special which could cause the objects in the database invalid.

I am running 8.1.7.2.5 on Windows 2000, I upgraded this database from 8.1.6 month ago.


What could cause the objects in the database invalid. and how to trouble shoot this problem.

Please advise