php出现Unable to load dynamic library 'c:\php\extensions\php_mssql.dll'

PHP Warning: Unknown(): Unable to load dynamic library 'c:\php\extensions\php_mssql.dll' - Access is denied. in Unknown on line 0 
 
 1\ 要将c:\php 的 dlls的ntwdblib.dll  复制到system32下. 而且有执行权限