I had a mistake in my problem definition. I have fixed it now. The code runs fine now. Below is the new code
a=[450;400;250;200]; % test input
b=[750;500]; % test input
n = 4;
m = 2;
oness=ones(m,1);
f = -(kron(a,oness))';
cont1=kron(eye(n),oness');
cont2=-cont1;
cont3=kron(a',eye(m));
A=[cont1;cont2;cont3];
bb=[ones(n,1);-zeros(n,1);b];
lb = zeros(m*n,1);
ub = [ones(m*n,1)]; % enforces binary
intcon= 1:8;
Aeq = [];
beq = [];
x = intlinprog(f,intcon,A,bb,Aeq,beq,lb,ub)