IIS 8 Eventlog access when running website from UNC path

Hi,

I have a strange problem with my IIS 8/.NET 4.0 website on windows server 2012 R2 when run from an UNC path (\\fileserver\wwwroot\site).
I cannot log errors in the eventlog. I get following error:

System.ComponentModel.Win32Exception: Access is denied

I have created the eventsource and can log into the eventlog when I am running the website localy (c:\inetpub\wwwroot) on the webserver.
It works from the unc path when run as an administrator. But that is not an option ;)

I have tweaked the registry permissions and also used caspol.exe to no avail.
Even sysinternals procmon.exe (which always solves such annoying problems) finds no Access denied.

Any help & ideas appreciated as this is driving me mad.
Br,
Jan