Why does my for-loop nested in an if-statement not work?

I have an for-loop inside an if-statement nested again in another for-loop (I know sounds complicated, example below), which seems to run perfeclty, as long as until the loop is called the SECOND time. Then it gives me the error:

Index exceeds matrix dimensions.

Error in code (line 50)

imb=squeeze(B_proc(n,:,:));

Does anybody have an idea why?

Here the simplified for-if-for-loop:

k=1; for i=2:length(proc_core) proc=cell2mat(proc_core(i,2)); sz=size(proc); l=sz(1); vs=cell2mat(proc_core(i,3)); if sz(2)==512 && sz(3)==512 && vs==2.5 kl=k+l-1; Core_proc(k:kl,:,:)=proc; k=k+l; elseif vs==2.5 for n=1:length(proc) imb=squeeze(proc(n,:,:)); imb=imresize(imb,[512 512]); Core(k,:,:)=imb; k=k+1; end end end

[Walter Roberson]

duplicated by later more complete http://www.mathworks.com/matlabcentral/answers/296421-why-does-my-for-loop-nested-in-an-if-statement-not-work