The Register Now button cannot be selected. It is grayed out

Description

After opening the Desktop Administrator and clicking the 'Register Single Use and Extensions' folder, the Register Now button on the right cannot be selected because it is grayed out.

Cause

This is caused by the user not having Administrative privileges on the machine. Administrative privileges are required to register ArcGIS Desktop.

Solution or Workaround

Note:
Administrative privileges are only required to register the software, but not to run it.