You need to close the figures that open automatically, when you import an image. Once the figures have been closed the button should be available.
Thanks for answering DrDre - do you mean the fields next to “Number of color spaces” and “Smoothing parameter”? If so those have numbers in already when opening the application, and any attempt to delete them just lead to numbers (10 and 0.1, respectively) coming in automatically once you leave the field, and the button still not being available.