log4net FileNotFoundException

For the longest time I was getting a FileNotFoundException debugging on my local when trying to use log4net in an aspx app. I would always break on ConfigureAndWatch in the Global.asax. Since I knew log4net was working, and the correct version was loaded from the GAC, I aways just hit "continue" and never spent any time on it.

Today I noticed log4net itself appeared in the call stack when this exception was thrown. This is odd, the assembly is throwing an exception looking for itself. I loaded the debug symbols for both log4net and the system assemblies, which is a great thing to be able to do, and found it was thrown from System.Type.GetType which was being used to dynamically load the PatternLayout class from log4net. Somehow this was incorrectly specified in the logging.config file I used to configure log4.net. Somehow log4net was not smart enough to know I incorrectly specified a loader, and the system exception, that the assembly could not be found, was being thrown.