The specified CGI application exceeded the allowed time fo..

I'm getting this error after 5 minutes (300 seconds) of processing a
PHP file in IIS 5.1 (WinXP).

I've searched for hours and every solution is the following:

Open the Administrative Tools control panel.
Open the Internet Services Manager item.
Right-click on the computer icon in the left panel and choose
Properties
from the menu that appears.
Click "Edit..." next to "WWW Services".
Click the "Home Directory" tab.
Click the "Configuration..." button.
Click the "Process Options" tab.
Enter a large value in the CGI script timeout field, perhaps 999999.


I've done this, and rebooted, and did it again, checked it, did it with
a script, etc. etc.

But still I get the error after 5 minutes. Are there any other
solutions or anything else? I also have the max_execution_time variable
in php.ini set to a high value, even though I don't think that's the
problem (it would give a php error instead).