imread error: Unable to determine the file format.

EDIT:: problem solved, reason for crash is corrupted image files.

i have the following code, it calculate the mean image of multiple of images (under frames folder)

i tested the same code with 40 images and it worked fine.

cd '/Users/macuser/Desktop/frames/';

fileList= dir('frame*.png');
listLength= length(fileList);

im= rgb2gray(imread(fileList(1,1).name));
sumImage= double(im);

for i=2:listLength
    grayImage= rgb2gray(imread(fileList(i,1).name));
    sumImage = sumImage + double(grayImage);
end;

meanImage = sumImage/listLength;
listLength
imshow(meanImage,[]);

however when i tested it with 100 images i get the error [Unable to determine the file format.]

Error using imread (line 362)
Unable to determine the file format.

Error in framesMean (line 24)
    grayImage= rgb2gray(imread(fileList(i,1).name));

i've tried to trace the error, line 24 which is causing the error works fine when i get it out of the loop.

fileList(i,1).name gets the full file name including the file extension ( png).

i can't find the cause of the error. any help would be appreciated.

[Image Analyst]

What is the i value when it crashes? What is the filename when that happens? Can you attach that image here? It seems to be corrupt. Can you open it in Photoshop?

[norah ik]

i came back to clarify, its working now.

seems like what you said, i noticed the counter i stopping at value 31, i checked that file it seems to be corrupted.

i regenerate the frames out of the video again and its working fine now with over 400 frames.

thanks a lot.