The HTTP Filter DLL php5isapi.dll failed to load

Symptoms: 

- In the ISAPI filters of IIS, the php5isapi.dll with set the filter to "PHP" show red arrow pointing down and for priority it says *unknown*

- In event viewer under application shown these two errors.

   "Could not load all ISAPI filters for site/service. Therefore startup aborted."

   "The HTTP Filter DLL C:\php\php5isapi.dll failed to load. The data is the error."


Cause:
IIS user account doesn't have sufficient permissions to the php files & folders

Solution:
Add IUSR_computername account permission for all the php files and directories

Note:
You need to restart PHP on IIS to reload