Error in blockproc function

whenever i use blockproc function in matlab it gives error as Undefined variable "internal" or class "internal.images.IOContainer". Error in blockproc (line 186) a = internal.images.IOContainer(a,'r');

i have tried all the possible combinations for blockproc, even a simple anonymous function handle could also produce error of the same type. plz help me come out of this. i'm also providing the code where i have to use blockproc

R = double(rgbImage(:,:,1)); B = double(rgbImage(:,:,3)); G = double(rgbImage(:,:,2)); I = (76.245 * R + 19.685 * G + 29.071 * B) / 255;

In = I / 255; % normalize to the range [0 1]

LumEnh = @(block_struct) histeq(block_struct.data);

% LumEnh = @(block_struct)IntensityCDF(block_struct.data);

L = blockproc(In,[3,3], LumEnh);