When an error condition arises as the dataset provider tries to post a record in the delta packet, an OnUpdateError event occurs. If the provider can't resolve an update error, it temporarily stores a copy of the offending record. When record processing is complete, the provider returns a count of the errors it encountered, and copies the unresolved records into a results data packet that it passes back to the client for further reconciliation. 

In multi-tiered applications, this mechanism lets you handle any update errors you can resolve mechanically on the application server, while still allowing user interaction on the client application to correct error conditions. 

The OnUpdateError handler gets a copy of the record that could not be changed, an error code from the database, and an indication of whether the resolver was trying to insert, delete, or update the record. The problem record is passed back in a client dataset. You should never use the data navigation methods on this dataset. However, for each field in the dataset, you can use the NewValue, OldValue, and CurValue properties to determine the cause of the problem and make any modifications to resolve the update error. If the OnUpdateError event handler can correct the problem, it sets the Response parameter so that the corrected record is applied.