Create Event in Eventlog

I am attempting to write an Event to an Custom Eventlog on Windows 2008 R2 Server.
It's for an C# application which runs under the Standard User context, so i gave access to the Eventlog to an AD Group which includes the allowed users.
The steps how made that are described here:
http://technet.microsoft.com/en-us/library/cc722385(WS.10).aspx
(Under the “Delegating access to the event logs” section.)

In my application I receive the following error message:
System.Security.SecurityException: Requested registry access is not allowed.
When I am using the eventcreate tool it works successfully as long as I do not specify the source .
When I do attempt to specify the /so parameter with "eventcreate", I receive
"ERROR: Access is denied"

Because my C# application was pointing to an "registry acces is not allowed" I gave rights for the group on the eventlog section in the registry but thats not working either.

So does anyone knows how to solve that problem??