Click moves mouse but doesn't actually click; getting runtime version WARNING

[Coehill]

I am running my script.ahk which contains the following:

Sleep, 1000       ; sleep for 1 second
Click, 3833, 500 ; click once at given coordinates
Return                ; exit

During the sleep, I select the window which will be clicked, then the script moves the mouse to the desired position. However, it never actuall clicks. I've tried adding a Click, 2 just to be sure and I'm still getting the same thing. Here is the output when running from terminal:

$ ironahk script.ahk 
WARNING: The runtime version supported by this application is unavailable.
Using default runtime: v4.0.30319