ERROR 001334: Cannot delete required field <field>

Error Message

In some instances, when attempting to delete a field from an attribute table, the Delete Field option is disabled. Attempts to delete the field using the Delete Field tool return the following error message:

Error:
ERROR 001334: Cannot delete required field <field>

Cause

This error occurs because the Field IsRequired (optional) option is checked when creating the field using the Add Field tool. Required fields are permanent by design and cannot be deleted.

Solution or Workaround

As a workaround, export the attribute table using the Feature Class To Feature Class tool, and remove the desired field in the Field Map (optional) section. Complete the steps below to do so:

1. In ArcMap, navigate to ArcToolbox > Conversion Tools > To Geodatabase > Feature Class to Feature Class.
2. In the Feature Class to Feature Class tool window, select the feature class with the required field as the Input Features.
3. For Output Location, specify the geodatabase location of the layer.
4. For Output Name, specify a name for the output feature class. In this example, the output name is New_Feature_Class.
5. In the Feature Class to Feature Class window, under the Field Map (optional) section, expand the desired field and click it. Click the Remove button.
6. Click OK.

Note:
Exporting the feature class to a geodatabase from the Catalog window also opens the Feature Class to Feature Class tool window.
Using the Feature Class to Feature Class tool creates a new instance of the attribute table, and the required field in the original attribute table is not removed.