If your PHP is configured as ISAPI module then the COM object you create in ur php page will use the same memory space as the web server. If your COM object takes too much memory then this may force some COM error as PHP does not handle the memory usage of COM itself. And also Web server doesnt know what do to free COM memory. But if you use PHP as CGI then PHP itself handle the memory usage of COM. Once in a script where i used COM and PHP as ISAPI module i got unknown COM error.But when i used PHP as CGI there was no error. So those who want to use COM object in your application please be careful about it.