Queries, trends, and reports generally have multiple dependencies upon each other. Modifying some elements within one resource can affect another. If modifications to a resource impact another to the extent that the dependent resource is rendered unusable, errors are reflected in the ArcSight Console. ESM manages and updates most of these resources and dependencies automatically, but not all.
For example, a trend built on a query relies on a set of fields (columns) contained in the base query. If you modify fields in the base query that are used in the trend, the trend is disabled. Similarly removing a resource (like a query) that another resource (like a report) depends on generates error messages on the ArcSight Console.
Caution: Instead of modifying the trend's base query, the proper approach is to create a different query, then create a new trend using that query.