AppDomain.CreateInstanceAndUnwrap not working in a website

Question

I have a very simple class CompiledFunction (MarshalByRefObject) - I try to create an instance of this in a new domain like so

var appDomainSetup = new AppDomainSetup();
appDomainSetup.ApplicationBase = Path.GetDirectoryName(typeof(CompilerService).Assembly.CodeBase);
var evidence = AppDomain.CurrentDomain.Evidence;
SandboxDomain = AppDomain.CreateDomain("Sandbox", evidence, appDomainSetup);

CompiledFunction<T> result = (CompiledFunction<T>)SandboxDomain.CreateInstanceAndUnwrap(
    assemblyName: typeof(CompiledFunction<T>).Assembly.GetName().Name,
    typeName: typeof(CompiledFunction<T>).FullName);

This works fine in a Console application, but in an ASP .NET MVC application I get the following exception - can anyone offer any suggestion as to why this is not working in a web app? The T parameter I am passing is System.Decimal

System.IO.FileLoadException was caught
  Message=The given assembly name or codebase, 'Ems.Scripting, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null', was invalid.
  Source=mscorlib
  FileName=Ems.Scripting, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
  FusionLog==== Pre-bind state information ===
LOG: User = EMSLaptop\PeterMorris
LOG: DisplayName = Ems.Scripting, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
 (Fully-specified)
LOG: Appbase = /C:/Users/PeterMorris/Documents/Visual Studio 2010/Projects/MvcApplication26/MvcApplication26/bin
LOG: Initial PrivatePath = NULL
Calling assembly : (Unknown).
===
LOG: This bind starts in default load context.
LOG: Found application configuration file (C:\Program Files\Common Files\Microsoft Shared\DevServer\10.0\WebDev.WebServer40.exe.Config).
LOG: Using application configuration file: C:\Program Files\Common Files\Microsoft Shared\DevServer\10.0\WebDev.WebServer40.exe.Config
LOG: Using host configuration file: 
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 /C:/Users/PeterMorris/Documents/Visual Studio 2010/Projects/MvcApplication26/MvcApplication26/bin/Ems.Scripting.DLL.

  StackTrace:
       at System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
       at System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
       at System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection, Boolean suppressSecurityChecks)
       at System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection)
       at System.Activator.CreateInstance(String assemblyName, String typeName, Boolean ignoreCase, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes, Evidence securityInfo, StackCrawlMark& stackMark)
       at System.Activator.CreateInstance(String assemblyName, String typeName)
       at System.AppDomain.CreateInstance(String assemblyName, String typeName)
       at System.AppDomain.CreateInstanceAndUnwrap(String assemblyName, String typeName)
       at System.AppDomain.CreateInstanceAndUnwrap(String assemblyName, String typeName)
       at Ems.Scripting.CompilerService.Compile[T](String[] scripts, Dictionary`2 variableDefinitions, IEnumerable`1 referencedAssemblies, ICompiledFunction`1& function, IEnumerable`1& compilerErrors) in C:\Data\EMS\Lib\Ems.Scripting\CompilerService.cs:line 43
  InnerException: 

Answer 1

The problem was that the Assembly.Code base started with file:///{rest of path here} - when using Path.GetDirectoryName on such a path it replaces file:/// with a single forward slash; so you end up with "/c:\myfolder\myfile.dll"

Getting Uri to tell me the local path was the solution

if (SandboxDomain == null)
{
    var appDomainSetup = new AppDomainSetup();
    string appBase = typeof(CompilerService).Assembly.CodeBase;

    //Added the following line
    appBase = new Uri(appBase).LocalPath;
    appDomainSetup.ApplicationBase = Path.GetDirectoryName(appBase);
    var evidence = AppDomain.CurrentDomain.Evidence;
    SandboxDomain = AppDomain.CreateDomain("Sandbox", evidence, appDomainSetup);
}

Answer 2

Looks like you did not properly copy Ems.Scripting assembly for web project or set wrong ApplicationBase for your new domain (more likely).

Path.GetDirectoryName call is suspicious in computing ApplicationBase property.