[PHP-INST] (Error) Premature end of script headers

[H.M.]

Hello,

I've installed PHP 4 (Windows) on an Apache Server.
I can run simple commands like :
<?php
print("hello");
?>

but commands sch as
<?php
phpinfo()
?>

generate an INTERNAL SERVER ERROR: In the Error log file I get the 
following explanation:
Premature end of script headers : c:php/php.exe

Can anybody help?