1. The GcMultiRow.CellErrorTextNeeded event occurs only when the GcMultiRow control's GcMultiRow.DataSource property is set or its GcMultiRow.VirtualMode property is true. Handling the GcMultiRow.CellErrorTextNeeded event is useful when the user wants to determine the cell error depending on its value or state.
2. When the user handles the GcMultiRow.CellErrorTextNeeded event and specifies error text in the handler, an error glyph appears in the cell unless the GcMultiRow.ShowCellErrors property is set to false. When the user moves the mouse pointer over the error glyph, the error text appears in a ToolTip.
3. The GcMultiRow.CellErrorTextNeeded event also occurs when the value of the Cell.ErrorText property is retrieved.
4. The user can use the CellEventArgs.RowIndex (or CellEventArgs.SectionIndex) and CellEventArgs.CellIndex (or CellEventArgs.CellName) and the CellEventArgs.Scope property to determine the state or value of a cell. They can also use this information to change or modify the ErrorText property. This property is initialized with the value of the cell ErrorText property, which the event value overrides.

System.Object
   System.EventArgs
      GrapeCity.Win.MultiRow.CellEventArgs
         GrapeCity.Win.MultiRow.CellErrorTextNeededEventArgs

Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

CellErrorTextNeededEventArgs Members
GrapeCity.Win.MultiRow Namespace
RowErrorTextNeeded Event
CellErrorTextNeeded Event