(Somebody with more insight will probably be along soon.)
The most likely cause of the 'headers already sent' warnings is whitespace after the closing tag (?>) in one of the php files. Start by looking at files that you may have edited – some editors will add a blank line at the end, which you definitely don't want.
You can remove that final php closing tag from the end of such files (the end-of-file implies the end of php) and then the problem can't recur.
Edit to add: What is the origin of that file 'sa_welcome.php' (shown in the warning message)? Is it legitimate or something that has been planted on the server?
The most likely cause of the 'headers already sent' warnings is whitespace after the closing tag (?>) in one of the php files. Start by looking at files that you may have edited – some editors will add a blank line at the end, which you definitely don't want.
You can remove that final php closing tag from the end of such files (the end-of-file implies the end of php) and then the problem can't recur.
Edit to add: What is the origin of that file 'sa_welcome.php' (shown in the warning message)? Is it legitimate or something that has been planted on the server?
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Nick.
Nick.