Error: 999999 CodedValueDomain already exists

While using the Table to Domain geoprocessing tool the tool fails to run and the following message is displayed:

Domains define a range of values that can be used for multiple attribute fields. Usage of domains helps to know data coherence by limiting the choice of values for a particular field. By restricting field values found in drop-down lists, the coded value domains is been created. Range domains are automatically validated during editing.

But sometimes duplicate code value is created which leads to the above error (Error: 999999: Error executing function. The value is added to the CodedValueDomain already exists)

To correct the error the duplicate code value should be removed. The best way to remove the duplicates is to use the Delete Identical tool.

Use Arc Toolbox >Data Management Tools> General and run the Delete Identical tool.

Once the duplicate code value is removed, run the Table to Domain tool again for its successful launch

Note:

A coded value domain specifies a set of values in the attribute that can apply to any data type like text, numeric, date, and so on. For example, a coded value list for a text attribute might include Road types values: ML - Metallic road; NML - Non-Metallic Road; RC - Rough concrete road, or a coded value list might include the numeric values representing permitted speed limits: 30-50; 50–70; and 70-90.