In my previous entry detailing the process of setting up the AIF File System Adapter XML Export Capabilities, I mentioned the problems that I had been having with not being able to export the picking list through the readPickingList action. It turns out that if you have 'LogisiticsRegistration' configuration key enabled and you have the 'Set inventory transactions to picked' option unchecked, you will get the same errors that I received. Apparently this option doesn't check itself by default when you enable the LogisticsRegistration config key. The option is located at the following form: Accounts receivable -> Setup -> Parameters -> Update Tab.
Check the option, recreate a sales order, post the picking list and then you will be able to export it through the 'Inquries' button.
Note: This will not allow any Picking Lists posted previous to the option change to be exported.