Validation For Duplicate Materials (Syclo Inventontory Manager 4.2)

Hi experts,

I am working on inventory manager 4.2 (SMP 3.0 SP 08).

While doing unplanned inventory count, we can add a material only once. Again, when adding the same material, after transmit, I am getting error 'XXXXX with stock type (X) already exists' which is standard in SAP ECC too.

I want to do the same validation in screen level wherein, when adding the same material again, the validation rule should get triggered.

I am trying to add the below validation rule in MaterialAdd transaction.

It's not working. Can anyone help me on this?

Regards,

Bino