unlink error for user pictures

On logging in users are getting:

"warning: unlink(sites/default/files/imagecache/user_image_default/userpics/picture-27.jpg) [function.unlink]: Permission denied in /home/kristina/qwodev/includes/file.inc on line 435.
warning: unlink(sites/default/files/imagecache/user_image_large/userpics/picture-27.jpg) [function.unlink]: Permission denied in /home/kristina/qwodev/includes/file.inc on line 435."

Imagecache 6.x-2.0-beta10
Imagecache Profiles 6.x-1.1
Drupal 6.15