Purchase requisition: Category drop-down blank when selecting non-catalog items

Hi all,

I am attempting to set-up requisitioning of non-catolog items on AX2009. We buy services such as maintenance for which we don't want to set up specific items, so have set up some generic service items.

So far, I have done the following:

1. Created generic service items for things like general non-stocked stationery etc.
2. Created a product group hierarchy as follows (will be expanded further in the future)

When I attempt to select a "Category" for the non-catalog item I am purchasing in the purchase requisition add item form, the drop-down is blank.

Strangely, I can type in my "Category" name and then the category will be successfully returned, but for some reason, it is not shown in the drop-down. Any ideas as to why the drop down is blank?