SerializationException after setting a LogicalThreadContext property

I have found that accessing Page.Request.Url after setting a LogicalThreadContext property causes a SerializationException with the following message: Type is not resolved for member 'log4net.Util.PropertiesDictionary,log4net, Version=1.2.12.0, Culture=neutral, PublicKeyToken=669e0ddf0bb1aa2a'.

I have been able to reproduce the problem on two different machines with the following steps:
1. Create a new ASP.NET Empty Web Application
2. Add a reference to log4net.dll
3. Add a new Web Form
4. Add the following code to Page_Load:
log4net.LogicalThreadContext.Properties["Test"] = 1;
Uri url = Request.Url;
5. Hit F5