I'm trying to set the position of the Messages.app chat window using AppleScript.

```
tell application "System Events"
    set position of window 1 of application "Messages" to {100, 100}
end tell

```

With this code I get an error:

```
error "Messages got an error: Can’t set «class posn» of window 1 to {100, 100}." 
number -10006 from «class posn» of window 1

```

What does that mean?

If I try the same code with Finder it works. But most of the other applications don't work.