I'm not sure what could lead to that warning message (unless maybe you're logged into Windows as "Guest") or why running it with that command would suddenly allow the planner to display when double-clicking the file didn't work.
I have an idea for how to eliminate it, but it involves removing a feature, so I will have to ask others on the main thread about my planner to make sure it won't upset people.
In the meantime, making a batch file with that command should work for you.