What could be the problem, and how can I correct it??
First of all, upgrade PHP. You are using an old version, which is known
to have several bugs, that's why PHP 4.0.4pl1 was released shortly after
the release of PHP 4.0.4. I recommend upgrading to a more recent version
of PHP (note, if you do this you may need to tweak the php.ini file with
PHP 4.2.x distributions and above, see the mailinglist archives).
The error message says you need to look in the Apache error log. I
recommend doing this first and e-mail the relevent error messages to the
mailinglist (if it doesn't give enough hints how the problem can be fixed).