This happens when we are using RED, Revenue Expense Deferral. When you go to look up Vendors in the Deferral Inquiry window (Inquiry | Financial | Deferral) with the Purchase Order Processing Module selected, the window pulls up the Customers and Prospects window instead of the list of available Vendors in the company. To workaround this, Select the Payables Management Module from the dropdown first, then the Vendor option for the filter and then select the Vendors desired in the From and To fields. Then change the Module dropdown back to Purchase Order Processing and click Redisplay.