I also got the below run time error because of using the log4net dll. However, the reference to the dll was correct.
"ASP.NET runtime error: Could not load file or assembly 'log4net, Version=126.96.36.199, Culture=neutral, PublicKeyToken=1b44e1d426115821' or one of its dependencies. The parameter is incorrect. (Exception from HRESULT: 0x80070057 (E_INVALIDARG))".
The Solution is to clear the "C:\Windows\Microsoft.NET\