Weird behavior of exec()

Hi everybody. I need to use exec() to run a background php script, but it's not working properly. Take a look at this sample: a.php <? echo ' File A (1) '; exec('php b.php > output.txt &'); echo ' File A (2) '; ?> b.php <? echo 'File B'; ?> output.txt (begins with 64 null bytes before the following)

    File A (2)

I would expect the output's content to be "File B", but it's not happening. I came across this problem because I have a mailing application which stopped working after being moved to a new host. The messages were sent by a background script launched on user's demand. Like this: SendMessages.php <?

      ...
      exec('php Daemon.php -x ' . $USERID . ' > /dev/null &');
      ...

?> Now it won't work, and I got no clue about what's going on. What now? Thank you.