Unable to select an active attribute in planning area

Hi Team,

We made a copy of SAP3 planning area and associated MDT to it. We are unable to select (clicking does not help) attribute SXXPRDID in planning area as shown below:

SXXPRDID is associated with MDT, which are all active, that are used exclusively only for this planning area.

Please guide.

Regards,

Aditya G