PHP Warning: PHP Startup: Unable to load dynamic library 'C:\PHP\ext\php_mysqli.dll' - Access is denied

Hi. I've spent the last 6 hours researching this on the Internet and can't find a solution so I'm hoping someone might be able to help.

Anytime I use new mysqli() or mysqli_connect() I receive this error on my browser:

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PHP Warning: PHP Startup: Unable to load dynamic library 'C:\PHP\ext\php_mysql.dll' - Access is denied. in Unknown on line 0 PHP Warning: PHP Startup:
Unable to load dynamic library 'C:\PHP\ext\php_mysqli.dll' - Access is denied. in Unknown on line 0
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I have PHP 5.1.4 installed on WIN along with MySQL 5.0.22 running on IIS 5.1 (XP Pro). I have correctly updated the php.ini file with these modifications:

extension_dir = C:\PHP\ext
extension=php_mysql.dll (without semi-colon)
extension=php_mysqli.dll (without semi-colon)

I have placed the updated libmysql.dll file that I have downloaded from http://dev.mysql.com/downloads/connector/php/ in the C:\PHP, C:\WINDOWS and C:\WINDOWS\system 32, have restarted everytime and still cannot correct this error.

Does anyone have more information to assist me? If you need any more information from me to help diagnose, I will be glad to provide.

source: http://forums.mysql.com/read.php?11,102233,102233