Scratch that, I'm getting lots of these errors even with the latest trunk:
[Wed Jul 19 11:28:07 2006] [error] [client 192.168.1.105] PHP Warning: Cannot modify header information - headers already sent in Unknown on line 0
I've seen this error for weeks (months?) on my system; freebsd, apache2, php5, mysql 5 - but was told it was harmless, and assumed it'd be addressed. no I haven't checked if it's an entered bug - should have.
Sometimes they result in a blank message window, but generally I can go on browsing. I don't really get the pattern yet.
I haven't seen this in recent builds, even when the error shows up in the logs.
This is a common problem when one of the include file has a blank line (or any html) and when the code then try to set a header for the page.
I would look for any empty line after any "?>" or " ?php> " tag in any of the page or config file.
Thomas