"Microsoft no longer permits services running under System to interact with users."
More at http://social.answers.microsoft.com/Forums/en-US/vistaperformance/thread/ca139ba9-c96c-49af-bc09-83abc26f3f5d
And possibly a setting you can change is there. But the changes in the security model can burn.
I am trying to send a message from my Win XP Pro 32 bit machine to my Win 7 Pro 64 bit machine. However Interactive Services Detection is holding up the message until I respond to a prompt (Something like "Do you want to view the message?"). But when I disable Interactive Services Detection on the Win 7 machine, I don't receive the message at all. Is there a way to receive the intended message, but without the Interactive Services Detection prompt?