Error HTTP 500.0 - Internal Server Error

The Error HTTP 500.0 randomly happen on my server since a few weeks when I try to execute a php srcipt or ajax request. When the error appear I juste have to refresh and the php script works normaly.
I'm using Windows Server 2012 R2, IIS v8.5 and PH v5.6

Here's the detail of the error:

Modul : FastCgiModule
Notification : ExecuteRequestHandler
Gestionnaire : PHP_via_FastCGI8
Error Cod : 0x800703e3

This error happend every 5 minutes, I have read and test every posts I could find on forums but nothing worked.
I have set the MAX_FCGI_MAX_REQUESTS Value to 10000.
The handler mappings on IIS looks OK php-cgi hanler mappings

I really need help.