Static Constructor is called twice in the same appdomain?

It looks like you managed to load two separate instances of log4net into the same AppDomain.

One project references:

<Reference Include="log4net">
  <HintPath>..\packages\log4net.1.2.11\lib\net35-full\log4net.dll</HintPath>
</Reference>

The other:

<Reference Include="log4net, Version=1.2.10.0, Culture=neutral, PublicKeyToken=1b44e1d426115821, processorArchitecture=MSIL">
  <SpecificVersion>False</SpecificVersion>
  <HintPath>..\ExternalReferences\log4net.dll</HintPath>
</Reference>

One of them is strongly named, the other isn't, this resulted in .net giving them different identities. And the hint path differs too. Also one seems to be 1.2.10, the other 1.2.11.

try calling AppDomain.GetAssemblies() and check if log4net occurs twice.