Fluid Mask has greyed out and I can access the plug-in in Photoshop?
Photoshop will disable the plug-in if the image in question is not suitable for use with Fluid Mask. Fluid Mask 1.0 requires images be 8-bit per channel rather than 16. Both Fluid Mask 2.0 and 3 can handle 16-bit images. The image data will also need to be in either RGB or CMYK mode, so you may need to convert the image to one of these modes prior to use. Greyscale images, for example, cannot be loaded into Fluid Mask.