Workflow Types; User Defined page; Parameters grid is disabled even when 'Custom Parameters' selected

The Paramters grid on the User Defined page of the Workflow Types form was disabled, even when an Entry Type of 'Custom Paramters' was selected.

This is due to an Entry Type of 'Parameter Set' having previously been selected and a Parameter Set specified. To remedy this, re-select an Entry Type of 'Parameter Set', clear the specified Parameter Set and then change the Entry Type back to 'Custom Parameters'.