This had me stumped for a while. My initial thought was to subclass
FileAppender or RollingFileAppender and override ActivateOptions. You can't do
that because the error happens during the XML configuration processing. What
you need to do is write a PatternString to Boolean adapter for the XML
The properties you are using to create the logfile name, are these being
generated by log4net? If they are, I dont think you are going to succeed, the
logfile needs to be created prior to logging commencing. The properties you
seem to be supplying wont exist at the point the you are trying to
