Using the following SQL statement in the Select By Attribute dialog to query blank records in a shapefile or coverage will cause ArcMap to crash:
Using an operator (=, -, *, /) will prevent the crash, but no records will be returned.
This is a known issue.
For all versions of ArcGIS, use two single quotes to query for blank values in a string field and a zero to query for blank records in a number field. For example:
"StringField" = ''
"NumberField" = 0
Shapefile and Coverage attribute tables are not capable of storing NULL values in number and string fields, only NULL dates are permitted. ArcGIS does not recognize NULL date values.