Photoshop Issues: When I tried to launch a plug-in from Photoshop, I received the error that the plug-in was “not currently available.” What does this mean?

This error occurs when a plug-in is launched from the Selective Tool before an RGB image is opened. Open an image before accessing the plug-in in order to prevent this error. If you already have an image opened, then make sure it is an RGB image, as opposed to a CMYK or Grayscale image, as the plug-ins will only open images in the RGB color space.