The shortcut command+tab (Γîÿ + ) is used by the System from Mac OS 8.5
Although it's a nice addition, you might want to use this shortcut for Wapp pro's own shortcuts.
To do so, you'll have to disable the system shortcut. Just run the script. If the shortcut is enabled, you'll be asked if you want to deactivate it. Once the shortcut is deactivated, you can re-activate it whenever you want by launching the script once again.