Hello.  I'm new to Salesforce and am following the tutorials in the Force.com Workbook.  The lesson is to create a flow to add a Line Item to an existing Invoice when you press a custom button.  Instead of getting a new page for the new Line Item, I get the "URL no longer exists" page.

This is the URL on the error page:

https://na17.salesforce.com/flow/Add_Line_Item_from_Invoice_and_Update_Stock_Quantity%E2%80%8B?vInvoiceId=a01o0000001EMeC&retURL=/a01o0000001EMeC

And this is the URL in the custom Button definition to launch the flow:

/flow/Add_Line_Item_from_Invoice_and_Update_Stock_Quantity?vInvoiceId={!Invoice__c.Id}&saveURL=/{!Invoice__c.Id}&retURL=/{!Invoice__c.Id}

I'm only following the workbook instructions.  I would also appreciate help in finding the exact error message.

Thank You