Call to vbscript subroutine fails if not in standards mode.

I call a simple subroutine from an HTML button (onclick="vbscript:ShutDownSys") in an HTA.  This works fine in compatability mode but when I add <meta http-equiv="X-UA-Compatible" content="IE=9" > I get "ShutdownSys is undefined".  Removing the meta tag restores the status quo. I'm trying to us some CSS3 features.  Any ideas?

Regards,  Giles Marshall