If your default Photoshop settings are not standard, you may get the message, "Command "Invert" is not available" when trying to run some of the RA Panels' scripts that involve that command.
To stop this from happening and allow our scripts to run correctly, please change some of the default layer mask settings in your Photoshop.
There are two places where this same setting can be fixed.
Option #1: Options in the Layers Palette
Click the menu icon in the top-right corner of the Layers Palette and select Panel Options.
In the Panel Options dialog box, make sure the "Use Default Masks On Fill Layers" box is checked.
Option #2: Options in the Adjustments Palette
Select the background layer in your PSD, then click the Adjustments Palette menu icon as pictured below.
Make sure the "Add Mask by Default" option is checked.