problem with php_mssql.dll

[gluck4]

Configuration: Windows 2003, IIS 6, PHP as CGI, MSSQL SERVER 2005, MySQL. User IUSR_HOST has full access to php directory.

Problem: when i use extension=php_mssql.dll in php.ini, appears mistake
[code]PHP Warning: Unknown(): Unable to load dynamic library 'c:\php\extensions\php_mssql.dll' - Access is denied. in Unknown on line 0[/code]

MySQL too stops to work. IIS writes:
[code]The specified CGI application misbehaved by not returning a complete set of HTTP headers.[/code]

Without extension=php_mssql.dll all work, except MSSQL.