how do I work around log4net keeping changing publickeytoken

We have an asp.net 4.0 project which uses a couple of frameworks which is dependent on log4net version 1.2.10.0. Today I tried to include a new framework which is dependent on log4net version 1.2.11.0, I've been stuck ever since:

log4net 1.2.10.0 has publickeytoken = 1b44e1d426115821

log4net 1.2.11.0 has publickeytoken = 669e0ddf0bb1aa2a

Since these are different i cannot use either assembly redirects (to make all frameworks use the same version of log4net) or codebase (to have just the new framework use version 1.2.11.0) through the runtime element in web.config.

What are my options here ?

(and why the bleep does log4net keep changing publickeytokens between versions, as I understand it a lost key was the reason for the switch between version 1.2.9.0 and 1.2.10.0, did they lose the key yet again? I'll volunteer my dropbox to keep it safe if they need it...)

Edit: Ok, so the log4net guys apparently had the idea that releasing with two keys was a good idea, but that means that every framework you make use of needs to agree on which of the two flavors they prefer, or those frameworks cannot work side by side in the same appdomain. Am I the only one finding this a horrible idea? if everyone did this then everything would break down, right?

Edit2: As I stated, I'm not using log4net in my business code, but I use several frameworks which depend on 1.2.10.0, and the problem arose when I tried to use a new framework which depended on 1.2.11.0 (new key), so Stefans answer doesn't apply, because the new framework will expect the new key, not the old one

This is how I got things working with version 1.2.11.0.

1. Curse apache for changing the key in the first place :)
2. Download the version of 1.2.11.0 signed with the old key.
3. Sort out your own code out by removing any direct references to log4net (new key) and replace with a reference to the assembly signed with the old key.
4. Sort out any dependant assemblies you may have by including this segment in your web/app.config

   <runtime>
        <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
            <dependentAssembly>
                <assemblyIdentity name="log4net" publicKeyToken="1b44e1d426115821" culture="neutral" />
                <bindingRedirect oldVersion="0.0.0.0-1.2.10.0"
                                 newVersion="1.2.11.0"/>
            </dependentAssembly>
        </assemblyBinding>
    </runtime>

I am using the latest version of log4net which I downloaded through nuget. However, one of the libraries that I'm using requires the old version. My troubles led me to this question.

The problem with the other answers are that they are using the same dll version for all bindings. I want to use features in the new version for everything else but the legacy dependency.

To be able to do that you need to do the following:

1. Start by downloading the old version (version of 1.2.11.0).
2. Rename the downloaded binary to log4net.1.2.10.dll. Include it in your startup project with Build action set to None and "Copy if newer"
3. Tell .NET where it can find the old version:

App.config

<runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
        <dependentAssembly>
            <assemblyIdentity name="log4net" publicKeyToken="1b44e1d426115821" />
            <codeBase version="1.2.10.0" href="log4net.1.2.10.dll" />
        </dependentAssembly>
    </assemblyBinding>
</runtime>

The href attributes identifies where the old version is. Hence all other requests for log4net will point on the new version.

You can download a version of log4net 1.2.11.0 that is signed with the old key. The reason why the changed to a new key is explained in their FAQ:

http://logging.apache.org/log4net/release/faq.html#two-snks

(Basically the new key is publicly available and for some reason they did not want to include the old key in the distribution. It is not clear to me why they did not just make the old key publicly available though)

Don't know is it suitable for your particular case or not, but you can recompile one of the frameworks, so they will use log4net with the same public key. In my case it was FluentNHibernate which uses log4net 1.2.10 and Combres with log4net 1.2.11 with new key. I downloaded log4net 1.2.11 signed with old key and recompiled Combress with it. After that added assembly binding redirect from 1.2.10 to 1.2.11 and it starts working.

This won't necessarily work in all cases, but because the project that was using log4net was OSS I downloaded the source, replaced the conflicting version of log4net with the version I was using and rebuilt the project. In my case it was Topshelf, so I now have a version of the Topshelf assembly that was built with the same version of log4net I'm using and now I can reference both without a problem.

I tried to go to the links provided above, but it seems like all the links in the Apache site are not working. Then this is what I did to resolve the issue:

From your Visual Studio, use Nuget to download and install the latest version of log4net (1.2.13.0). The NuGet package manager will automatically download and upgrade all the log4net(1.2.11.0) to the latest version.