Ran into the same problem. Using IIS 6 with PHP 5 and FastCGI. PHP is installed at C:\PHP manually using threading-unsafe manual deployment (see https://www.iis.com/php)
Made sure to add IUSR_COMPUTERNAME and “Network Service” to have read/execute access to C:\PHP. (This was already configured at the wordpress directory location.)
Modified php.ini so that instead of ‘./’ as the extensions directory it was ‘C:\PHP\ext\’. I had changed it to ‘C:\PHP\’ but apparently that was incorrect.
Also removed the comment (semi-colon) behind the mysql DLL,
.. from ..
;extension=php_mysql.dll
.. to ..
extension=php_mysql.dll
Start menu, Run…, “iisreset”
Works.
