"Server error" with mail()

I've got PHP4 running on NT4 and PWS4. I have a simple script that uses mail() but it stops with the message "Warning: Servor error in " followed by the name of the script and the line. This scripts works fine under Linux. In the php.ini the SMTP server has been setup properly AFAIK (I tried it with a local Windows mail server and with a remote Linux one, both working all right). Anyone knows the cause of this problem ? It has already been mentioned a couple of times in this NG, but no solution has been proposed so far. Thanks in advance Gilles Tran