EventLog.WriteEntry() Permissions issue

void Page_Error (object sender, EventArgs e) {
string errorMessage = "Error Occurred:" + Server.GetLastError(); 
Server.ClearError(); 
if (!(EventLog.SourceExists("myWebApp","."))) 
EventLog.CreateEventSource("myWebApp","System",".");

EventLogPermission eventLogPerm = new EventLogPermission(EventLogPermissionAccess.Administer,"."); 
eventLogPerm.PermitOnly(); 
EventLog evLog = new EventLog(); 
evLog.Source = "myWebApp"; 
evLog.WriteEntry(errorMessage, EventLogEntryType.Error); evLog.Close(); 
}