Из лога видно, что виртуальное приложение пытается загрузить сборку Castle.Windsor.
Использование сборки прописано в файле конфигурации, находящемся в корне сайта. Виртуальное приложение эту сборку не использует.
Как объяснить IIS-у, что он эту сборку для данного виртуального приложения грузить не должен?

LOG: This bind starts in default load context.
LOG: Using application configuration file: C:\inetpub\wwwroot\Custom Web Site\Authorization\web.config
LOG: Using host configuration file: C:\Windows\Microsoft.NET\Framework\v4.0.30319\Aspnet.config
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v4.0.30319\config\machine.config.
LOG: Policy not being applied to reference at this time (private, custom, partial, or location-based assembly bind).
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework/v4.0.30319/Temporary ASP.NET Files/authorization/31022d3e/718696f/Castle.Windsor.DLL.
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework/v4.0.30319/Temporary ASP.NET Files/authorization/31022d3e/718696f/Castle.Windsor/Castle.Windsor.DLL.
LOG: Attempting download of new URL file:///C:/inetpub/wwwroot/Custom Web Site/Authorization/bin/Castle.Windsor.DLL.
LOG: Attempting download of new URL file:///C:/inetpub/wwwroot/Custom Web Site/Authorization/bin/Castle.Windsor/Castle.Windsor.DLL.
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework/v4.0.30319/Temporary ASP.NET Files/authorization/31022d3e/718696f/Castle.Windsor.EXE.
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework/v4.0.30319/Temporary ASP.NET Files/authorization/31022d3e/718696f/Castle.Windsor/Castle.Windsor.EXE.
LOG: Attempting download of new URL file:///C:/inetpub/wwwroot/Custom Web Site/Authorization/bin/Castle.Windsor.EXE.
LOG: Attempting download of new URL file:///C:/inetpub/wwwroot/Custom Web Site/Authorization/bin/Castle.Windsor/Castle.Windsor.EXE.