Could security be at play here? It sounds like the application can’t “see” form “abc”. Can you open this form directly on the web? If it’s a Response form type, that may cause issues.
Your follow-up implies that you simply want to send an “Under construction” message to the browser. In this case, why not have a web agent that prints to the browser? For example, you could add WebQueryOpen code to your “xyz” form.