What is the reason for this error?

An attribute called model_name is added to an existing schema, customerModel, using the following code:

<attribute label="Model Name" length="255" name="model_name" type="string"/>

The XML for the new columns is parsed successfully and saved to the schema definition.

The end user tries to view the data using configure list… by adding the new attribute to the output columns. The following database error is thrown. “Invalid column name ‘sModel_name’”

What is the reason for this error?
A . The navtree definition for customerModel must be updated.
B . The end user must disconnect and reconnect from the Campaign client.
C . The attribute definition is missing a default value.
D . The Update Database Structure process was NOT completed successfully.

Answer: C