Flexfield Validation Values

Hello,

Trying to define a Flexfield Validation Values (N: Purchasing SuperUser > Setup > Flexfields > Valdation > Values). However, the entire form is greyed out and protected. I have already defined the PO Item Category Key Flexfield Segments and associated Value Sets.

Does anyone know why the system is preventing me from defining the validation values that correspond with each value set? I have attached a screen capture showing the form protected against update.

Thanks,

Anthony