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Contents 1 Errors 1.1 "Cannot modify header information"

[edit] Errors

[edit] "Cannot modify header information"

The PHP warning

Warning: Cannot modify header information - headers already sent

is caused, because there's output (from PHP) already, when there's a call to e.g. header(), which cannot send a HTTP header then anymore.

This is usually caused by e.g. adding newlines at the end of some file you've manually edited (e.g. a configuration file in /conf).

Usually the cause of the error is given in the error message itself:

Warning: Cannot modify header information - headers already sent by
(output started at /path/to/file/with/output:LINE)
in /path/to/file/with/warning on line X

Take a look at /path/to/file/with/output, especially at/around line LINE.

If there's no "output started at" info given, you're kinda out of luck. The only possible solution (apart from taking a look at the file's you've modified) seems to be adding manually echo "foo"; statements into the code to see if the error already gets triggered here (then the /path/to/file/with/warning and "line X" would change accordingly).