Weird permission issue

I have a PHP app and it runs from /var/www/html/foo. It writes to a log file in there log.txt. To do some testing I created a dir /var/www/html/foo.new and installed the code there. To switch back and forth I do this: mv /var/www/html/foo /var/www/html/foo.old mv /var/www/html/foo.new /var/www/html/foo When I do that I get an error writing to the log file: Error #2: fopen(/var/www/html/foo/log.txt): failed to open stream: Permission denied But if I switch back: mv /var/www/html/foo /var/www/html/foo.new mv /var/www/html/foo.old /var/www/html/foo I do not get the error. The code is identical in foo and foo.new and the perms and owner on log.txt is identical in too and foo.new. I have tried restating apache and rebooting the machine, but no joy. What could be causing the permission error?