Error when rebuilding Album thumbnails
 

In the AdminCP, when I click to rebuild the Album thumbnails, I get the following error:

Code:
Warning: fopen([path]/images/album/full/0/2adcfa3105a1c76f709449da4856dcdc_27.jpg) [function.fopen]: failed to open stream: Permission denied in [path]/includes/class_dm_picture.php on line 514
If it matters, PHP 'safe_mode' is off.

Please advise how I can fix this.