User is trying to create a recurring check, but cannot as the Source Check drop-down is empty.
This can happen if the Payee you selected does not have any associated checks that you can use as the Source Check for this recurring transaction. Another reason could be that you do not have any checks in Core to be used as the Source Check for this recurring transaction. Make sure you have created checks in Core before you can create recurring checks from them. Check the Core Help for details.