I have a CommonUtils lib I have built into a dll which I file reference from several of my projects. CommonUtils depends on log4net.dll which was set as a file reference and
When I've had a similar situation in the past, I received a compiler warning within Visual Studio telling me that I needed to add a reference to the dependent library.
Are you receiving such a warning when you compile? If so, follow the advice it gives and you should find Log4net copied to your output directory.