I have tried to create an item in Item Master Data, and only the "Purchase Item" box is checked.

The "Set G/L Account By" box in the Inventory Data tab is set at Item Level. The Item Group, indeed, has a Purchase Credit Account and so does the default warehouse.

But, when I try to add this item, an error message appears saying "Purchase credit account not defined for this item".

Why in the world is it saying this, and how to I fix this?

Thanks!