chmod() [function.chmod]: Operation not permitted

/home2/denver/public_html/kernel/_3sCore/CoreClasses/controller.inc.php line 150
handlegeneralerror("2", "chmod() [<a href='function.chmod...", "/home2/denver/public_html/kernel...", "150")
/home2/denver/public_html/framework/error/handler/debug.inc.php line 37
chmod("/home2/denver/public_html/cache/...", "511")
/home2/denver/public_html/kernel/_3sCore/CoreClasses/controller.inc.php line 150
displayimagecontroller.renderfile(OBJECT:beforeandafter, "after_photo", ARRAY[1])
/home2/denver/public_html/kernel/BeforeAndAfter/controller.inc.php line 7
displayimagecontroller.initialize()
/home2/denver/public_html/kernel/_3sCore/CoreClasses/controller.inc.php line 22
displayimagecontroller.page("225")
/home2/denver/public_html/kernel/_3sCore/CoreClasses/factory.inc.php line 24
beforeandafterfactory.getcontrollerclass("DisplayImage", "225")
/home2/denver/public_html/kernel/_3sCore/CoreClasses/factory.inc.php line 14
beforeandafterfactory.getcontroller("225")
/home2/denver/public_html/kernel/_3sCore/_3sApp/controller.inc.php line 82
_3sappcontroller.run()
/home2/denver/public_html/default line 47