problem with fuction handle evaluation in blockproc

I get the following error Function BLOCKPROC encountered an error while evaluating the user supplied function handle, FUN.

The cause of the error was:

Undefined variable block_struct.

Error in myfunction>calc (line 18) [row col]=block_struct.location;

I cant find why this happens.Is something wrong with handle creation?

function [ macroblock ] = myfunction( reference_frame,target_frame )

fun = @(block_struct,reference_frame) calc;

macroblock=blockproc(target_frame,[16 16],fun,'PadPartialBlocks',true)

end

function calc(block_struct,reference_frame 
[row col]=block_struct.location;
for i=1:16 %search constant
for j=1:16
  for p=1:16

   for q=1:16
      % SAD(i,j)=abs(struct.data(p,q,:)-reference_frame((row+p-1)+i,(col+q-1)+j,:))

    end

 end

end
end

 end