I have been trying to work through theCreate a Custom Block example/tutorial, using MATLAB/Simulink R2016b. In the second part, on creating a dialog to configure the custom block by creating a mask, when I reach the third pane ("Initialization") of the Mask Editor, I am supposed to mark the "Allow library block to modify its contents" checkbox. But the checkbox isdisabled (i.e.,greyed out). Why is the checkbox disabled? What can I do about this? Thanks.