I do not understand what this error is

guess=[pi/2 18]; M=[1 1 0 0 0 0]; %90 deg from home position to be along Y0 
for i=1:2*n 
    T(2,4)=y(i);T(1,4)=x(i);   
    Ti=ikine(r,T,guess,M,'tol',0.01,'pinv','alpha',0.01); % this is producing the error
     % Numerical method:0.01,"pinv" numerical method,0.001 step or increment 
    guess=Ti; 
x(i)=T(1,4);y(i)=T(2,4); %record x,y 
base(i)=Ti(1);arm(i)=Ti(2);control=[base;arm]; %save joint variable in a double array 
end

I am trying to do robot planning and trajectory and I keep getting an error saying

Error using SerialLink/ikine -Number of robot DOF must be >= the same number of 1s in the mask matrix

[Cam Salzberger]

The SerialLink and the ikine function are in Peter Corke's Robotics Toolbox, not the Robotics System Toolbox. I have updated the products and tags in this question accordingly.

I would suggest starting with that library's documentation, and searching using those keywords when looking for answers.

-Cam