Problem adding new subcategory to an incident category

Okay experts,

Quick question to ask. What happen when the "Link New Subcategories" button in grayed out. So you can not add a new subcategory to the incident.

These are the steps that I followed but as I stated above the button to link new subcategories is grayed out.

1. Click Incident Management > Configuration in the System Navigator.
2. Click Incident Categories and then click Search in the form that appears.
3. Select the Incident Category for which you want to add a subcategory.
4. Click the Subcategories tab in the Incident Category Definition page, and then click the Link New
Subcategories button.
5. Type a subcategory name.
6. Type a description for the subcategory.