There could be some dependency in newer released of Receivables with Order Management setup.

Following steps should fix the issue:

1. Create Inventory Organization (Item Validation) under the same operating unit that you are using with AR. This step is shown in Purchasing videos.

2. Assign the same Operating Unit to the seeded OM responsibility (or create a new OM responsibility if you like) that you are using with Receivables. Assign OM Responsibility to your user.

3. Setup Item Validation Organization in Order Management.
(N): OM -> Setup -> System Parameters -> Values
Query for Parameter 'Item Validation Organization'
Setup the Item Validation Organization from list of values.

This step is show in Order Management videos.