Core\PonghoException::chmod() [function.chmod]: Operation not permitted

On file /mnt/md1/home/rockanddoc/rockanddoc.com/pongho/application/libraries/flickr.php at line 208

#0 [internal function]: Core\{closure}(2, 'chmod() [_write_cache('http://www.flic...', 'a:2:{s:6:"photo...')
#3 /mnt/md1/home/rockanddoc/rockanddoc.com/pongho/application/libraries/flickr.php(35): Libraries\Flickr->_response('flickr.photos.s...', Array, false)
#4 /mnt/md1/home/rockanddoc/rockanddoc.com/pongho/application/controllers/media.php(9): Libraries\Flickr->get_random_image()
#5 /mnt/md1/home/rockanddoc/rockanddoc.com/pongho/system/action_controller/base.php(159): MediaController->index()
#6 /mnt/md1/home/rockanddoc/rockanddoc.com/pongho/system/core/pongho.php(174): ActionController\Base->run('index')
#7 /mnt/md1/home/rockanddoc/rockanddoc.com/pongho/system/bootstrap.php(33): Core\Pongho::run()
#8 /mnt/md1/home/rockanddoc/rockanddoc.com/index.php(109): include('/mnt/md1/home/r...')
#9 {main}