Error says "Non-MEX version doesn't support plusmin"

Hi Everyone,

I was trying to run this code:

clear all; clc; close all;
%Creating Pacman maze
canvas = zeros(300);
canvas(1:10,1:300)=1;
canvas(1:300,1:10)=1;
canvas(290:300,1:300)=1;
canvas(1:300,290:300)=1;
canvas(280:290,40:120)=1;
canvas(280:290,180:260)=1;
canvas(240:250,40:100)=1;
canvas(240:250,120:180)=1;
canvas(240:250,200:260)=1;
canvas(250:270,145:155)=1;
canvas(210:240,50:60)=1;
canvas(210:240,240:250)=1;
canvas(10:50,145:155)=1;
canvas(30:50,30:70)=1;
canvas(30:50,90:130)=1;
canvas(30:50,230:270)=1;
canvas(30:50,170:210)=1;
canvas(210:220,10:30)=1;
canvas(210:220,270:290)=1;
canvas(210:220,80:120)=1;
canvas(210:220,180:220)=1;
canvas(70:160,260:300)=1;
canvas(70:160,1:40)=1;
canvas(70:110,230:240)=1;
canvas(70:110,60:70)=1;
canvas(70:110,200:210)=1;
canvas(70:110,90:100)=1;
canvas(100:110,100:130)=1;
canvas(100:110,170:200)=1;
canvas(70:80,120:180)=1; 
canvas(80:110,145:155)=1;
canvas(130:160,120:180)=1;
canvas(180:190,120:180)=1; 
canvas(190:220,145:155)=1;
canvas(150:190,90:100)=1; 
canvas(150:190,200:210)=1; 
canvas(180:190,50:80)=1;
canvas(180:190,220:250)=1;
canvas(150:160,50:80)=1;
canvas(150:160,220:250)=1;
canvas(100:110,50:60)=1; %added manually 

idisp(canvas)
%Distance Transform command
goal = [200,251]; %goal point
start = [20,20]; %start point
dx = DXform(canvas); %create navigation object
dx.plan(goal); %create plan for specified goal
dx.query(start); %animate path from this start location

And I got an error saying

Error using imorph (line 69)

Non-MEX version doesn't support plusmin

Error in distancexform (line 124)

occgrid = imorph(occgrid, m, 'plusmin');

Error in DXform/plan (line 161)

dx.distancemap = distancexform(dx.occgridnav, dx.goal, dx.metric, show);

Error in Lab2Q5c (line 51)

dx.plan(goal); %create plan for specified goal

What do I do?