Hi,
If you are using the overloaded method EventLog.WriteEntry Method (String, String), then make sure that the first parameter, which is the event source associated with your event log, is already created and configured on the machine. Or is it a typo in that value?
If your event source is not present, then you can configure it using an EventLogInstaller or using the CreateEventSource method. See the following MSDN article:
http://msdn.microsoft.com/en-us/library/6w20x90k.aspx
Daniel.