Message: unlink(/tmp/ci_sessionaa51644b4360c8f6957d2c733): Operation not permitted

Server Throw this Error Periodically on localhost everything seems ok, I don't know why?

A PHP Error was encountered
Severity: Warning
Message: unlink(/tmp/ci_sessionaa51644b4360c8f6957d2c73286368e57f29f403): Operation not permitted
Filename: drivers/Session_files_driver.php
Line Number: 371
Backtrace:
File: /home/sandbox/public_html/dev/project-x/application/client/core/MY_Controller.php
Line: 15
Function: __construct
File: /home/sandbox/public_html/dev/project-x/application/client/controllers/Homepage.php
Line: 18
Function: __construct
File: /home/sandbox/public_html/dev/project-x/index.php
Line: 358
Function: require_once