If your data uses dates as part of database keys, some database dates cannot be written as NULL or illegal values. To write data that includes NULL or illegal values, the Connector converts the NULL or illegal date values used in keys to a value of 01/01/01 when writing data to some databases. Unfortunately, the code would not make a similar conversion when reading the same record, and those records written with 01/01/01 were not found. This could easily result in writing a record that cannot be read or deleted. When 4GL_CONVERT_DATE_ZERO is set to the default setting CONVERTED, the Connector locates and returns those records written using the date 01/01/01. This functionality can be disabled by setting the variable to UNCHANGED.