Re: How to specify Event Category when writing to EventLog?
The event category is a strange monster.
It's limited to being a System.Int16 so NLog converts it (or at least tries to). When you are specifying your layouts I'm guessing the conversion of those are causing an exception to be thrown and to be swallowed (unless you have nlog exceptions enabled).
Here's a 'short' (haha) article that quite a view blogs reference when asked how to setup Event Log categories.