Basis release field not editable

Hi,

I am trying to enter the basis release version for a logical system in my Application Architecture Model, however, the field is not editable in the Logical System Properties on the General tab in the Appl. details section. See screen shot attached. Does anyone know why this field is not editable for me? It appears editable, but it won't let you enter letters or numbers. Any help would be much appreciated. I'm using PowerDesigner v16.5

Thank you,

Tara