When trying to assign a part number to a symbol using the Select Part Number dialog, rows of empty cells appear in the top pane. Also, some part numbers known to match the applied filter may not appear, and double-clicking on a row causes the focus to jump to a different row or causes an unhandled exception.
This behavior can be caused by the presence of duplicate values in the Part_Number column in the table used for the parts database. This situation should be impossible since the Part_Number column should be the table's primary key, which requires unique values to be entered. In past cases, a different column or no column was found to be the primary key. In these cases, users had also been entering data using Microsoft Access instead of the Parts Database Manager.
Open the parts database using Microsoft Access.
Use the Find Duplicates Query Wizard or other methods to identify duplicate part numbers in the parts_database table. See Find and remove duplicate data.
Edit or delete records so that no duplicates remain.
Set the Part_Number column to be the primary key. This can be done by opening the parts_database table in Design View, right-clicking the Part_Number column, and choosing "Primary Key". This will prevent duplicate part numbers from being entered while using Microsoft Access to enter the data. Consider entering part number data using Parts Database Manager instead of Microsoft Access.
Save and close the database.
"Find and remove duplicate data" http://office.microsoft.com/en-us/access-help/find-and-remove-duplicate-data-HA010341696.aspx
keywords: Object reference not set to an instance of an object, Bentley.Electrical.UI.PartsDatabase.DSelectPart.gridViewAbove_DoubleClick