Inventory -

I am adding a new stock item. I have copied from a current item for size and range, I just need to add a new flavour.
When I add the price into the Selling Detail I receive an Error- The number of items per selling unit value cannot be zero.

I have tried various numbers, cases, items etc and I cannot move forward.

Note that I have copied the entry from the exact item in a different flavour and it is exactly the same. This leaves me not being able to add inventory items.

Any assistance would be appreciated.

thank you