Hi Stijn,
It is my understanding that you are using the first script as the InitFcn callback of your function block, then later in the function block you want to access the figure object created by the InitFcn script.
In this case, you can check that the variables defined in the InitFcn (Rectanglex,Object,etc) are all stored in the base workspace and hence the function defined by your block cannot access it directly. Hence the error pops up while you simulate the model. As a workaround you can consider using evalin function in your function block to access the required variables. As and example, see:
function MATLABFunction2(..)
coder.extrinsic('evalin');
obj = evalin('base','Object');
...
set(obj,...)
end
