RollingFileAppender fails if RollOverIfDateBoundaryCrossing required and current directory is not ApplicationBase directory.
RollOverIfDateBoundaryCrossing is called before the base class (FileAppender) ActivateOptions method is called. Therefore the File property has not yet been converted to a fully qualified path. If the current directory is not the ApplicationBase directory (e.g. when running under ASP.NET) then the RollFile call will fail with the message "Source does not exist" in the internal debug log.