rotate x tick label "error"

i am trying to rotate x tick label, so i use a file exchanger

it works one time but on another data it gives me an error:

 ??? Error using ==> text
Invalid parameter/value pair arguments
Error in ==> xticklabel_rotate at 159
       hText(cnt) =
       text(XTick(cnt),y(cnt),xTickLabels{cnt},...
Error in ==> CountWordFreq02 at 16
 xticklabel_rotate([],60,a(:,1));

this the code i am using:

 figure('color','w')
bar(cell2mat(a(:,2)));
set(gca,'XTick',1:size(a,1))
set(gca,'XTickLabel',a(:,1))
 xticklabel_rotate([],60,a(:,1));
% set(gca,'XTickLabelRotation',45)
set(gca,'YTick',0:1000:max(cell2mat(a(:,2))))
% set(a,'Rotation',90,'HorizontalAlignment','right')  
xlabel(' Top words');
ylabel('Frequency');
title('Hardware words frequency');

what is the error ? and if there is any idea to modify it ?

note: it seems that number of bars must be 31 or more to work...!