'Undefined constant false' and FastTemplates

PHP 4.02 ISAPI, Win2000, IIS 5. I'm using FastTemplates inside a class. The code is very simple, pretty much the same as the example code to initialise and print a FastTemplate in the docs. It works fine a few times, but if I leave the server for a few minutes (this seems to be important) and make the request again I'll get a warning: Warning: Use of undefined constant false - assumed 'false' in class.diary.php on line 267 and PHP dies with an access violation, requiring a restart of IIS. There's nothing remotely connected to the value 'false' anywhere. The object is being freshly created with every request and seems to be working fine. The offending line is $tpl = new FastTemplate($this->template_root); where the template_root variable is declared and valid. The other thing I'm concerned about is that just about any warning message appears to take down the server, and if I run php.exe from the command line any warning will cause a similar access violation - so I don't see that running it in CGI mode is going to help. Anyone seen different behaviour? Is PHP4 Windows actually stable? Julian.