I see that there is not much documentation for this above error. This is probably a configuration problem and can be easily corrected.
Warning: session_destroy(): Session object destruction failed
There is no session object in the first place.
Check whether the session data exists in the first place. Chances are that, the PHP configuration didn’t allow the session to start and hence session was not created. If this is the case, you would have first got errors similar to
Warning: session_start(): The session id contains invalid characters, valid characters are only a-z, A-Z and 0-9
session_start() permission denied.
You should check with your host to configure your session.
For the programmer:
Check out the PHP.ini file for correct session configuration. If everything seems to be correct, check for the session.save_path variable and whether that path is writable.
The session files are there in your session.save_path directory but PHP is not able to delete the files on logout.
Your permissions on the sessiondata directory are incorrect. PHP cannot delete the session file it has created. Set permissions on session.save_path directory so that the PHP user can delete files.