Thank you for your patience, NuclearMoose.
I’d better upgrade my searching skills…
Yes, I used EditPlus.
I searched the web and found a possible cause, that the PHP output buffering option was off. Does it make sense? I know little PHP…
And I noted some difference between my warning and the others: output started at /.header, not a php file. Does that explain something?
I got tons of such warnings… I checked the tags but they were ok. No whitespaces, no returns. Could someone help? The complete warning message follows:
Warning: Cannot modify header information – headers already sent by (output started at http://fengliang.3nv.com/.header:2) in /home/vhosts/fengliang.3nv.com/wp-login.php on line 7