Unable to create a new master data type

I am trying to set up a simple demo model on an On Premise S&OP on HANA system (Release 3).

I have created and saved some master data attributes.

But when I try and set up a new master data type, the system does not show any available master data attributes to select (even though 'All attributes' is selected in the dropdown), so I cannot save the new master data type.

Any suggestions regarding this problem are welcome...