I see that you get the error in 3rd line in the for loop not in the of 4rth line as you mentioned, I think your use case can be realized with the following code.
o = B(1:50,2);
for ind = 1:length(o)
a1 = diff(o);
c1 = find(a1>2^15);
e1 = find(a1<-2^15); %Error happens here
o(c1+1:e1) = o(c1+1:e1)-2^16; % Error doesn't occur here