What folder are you trying to save it in? I noticed you are not using fullfile() and trying to save into whatever the current folder happens to be. That's not as robust as saving it with the full folder and base filename and extension. If you hard code the folder name in there do you still get the error?
fullFileName = fullfile('d:\myImages\Behard', 'moosh.jpg');
imwrite(fullFileName);
You might have that file open in another program. Does it do the same after restarting MATLAB or the computer?
