adsense error message

Hi Dear,
I just tried to set up the adsense ads on a subsite but I received the following error message in italian which says that was not possible to save the settings. The server error message has a code 500.
"Spiacenti. Non è stato possibile salvare la tua configurazione. La richiesta al server non è stata eseguita ed è stato generato il codice di errore 500."

However, when I check the error log on the server I can see the following message.
[Tue Nov 22 01:51:20 2016] [error] [client 77.57.126.79:55602] - pixshopping.com - End of script output before headers: options-general.php, referer http://www.pixshopping.com/cristall/wp-admin/options-general.php?page=GooglePublisherPlugin

There is something I can do to solve this problem.
Thanks,
Paddy