It looks as if you didn't assign a value to the second input argument when you called the function. I also see that the first argument, X, is unused.
It seems possible you don't understand function call. If you have any doubts about how to pass values to functions, have a look at some of the introductory Matlab documentation, or a textbook, to get the idea - you'll find it very helpful to get this central idea completely clear.
By the way, this question seems closely related to your previous one, at
http://www.mathworks.com/matlabcentral/answers/587-low-pass-filter-for-image
It would be better to follow up that question rather than start a new one.
