PHP FastCGI HTTP Error 500 on Windows 7

I've just installed PHP (5.3.1) and MySQL (5.1.44) on my development machine. Then I used the Web Platform Installer to install a copy of Joomla and Drupal.

However, when I tried to browse either site application, I get a HTTP Error 500:

Module  FastCgiModule
Notification    ExecuteRequestHandler
Handler PHP_via_FastCGI
Error Code  0x00000000
Requested URL   http://localhost:808/drupal/index.php
Physical Path   D:\Projects\drupal\index.php
Logon Method    Anonymous
Logon User  Anonymous

PHPInfo.php reports that FastCGI is configured (not sure if that is significant). Sure the fact that PHPInfo.php reports anything is perhaps an indication that PHP itself is working...?

I'm struggling to know where to look for a solution... Each application appears to be configure similarly to my other [ASP/ASP.NET] applications.

From serverfault CJM

• Do you have custom error pages enabled?

  If so, IIS will replace the error output that PHP gives you with a custom error page. Try disabling that, et voila, there is your debug output.

  Probably a script error.

  CJM : No, custom error pages are not enabled. While it could be a script error, it would be a little surprising given that both Drupal and Joomla are similarly affected, and given that they were default installations from the Web Platform Installer (i.e. meant to be easy installs).
  From Matthias Vance