Ninject ASP.NET extension throwing TypeLoadException - asp.net

Question

I'm trying to use Ninject 3 in an ASP.NET webforms application. We've been using it without the Ninject.Web extension for a while by creating a new injection kernel everywhere we needed one. It didn't occur to me until now that that's not the right way to do things. I wrote a little test application that is successfully using Ninject.Web, but when I tried to do the same thing in our real application, I'm receiving a TypeLoadException as soon as the page loads. It doesn't even make it into my code where I can set a breakpoint. Here's the exception and stack trace:
Could not load type
'System.Runtime.CompilerServices.ExtensionAttribute' from assembly
'mscorlib, Version=4.0.0.0, Culture=neutral,
PublicKeyToken=b77a5c561934e089'.
Description: An unhandled exception occurred during the execution of
the current web request. Please review the stack trace for more
information about the error and where it originated in the code.
Exception Details: System.TypeLoadException: Could not load type
'System.Runtime.CompilerServices.ExtensionAttribute' from assembly
'mscorlib, Version=4.0.0.0, Culture=neutral,
PublicKeyToken=b77a5c561934e089'.
Source Error:
An unhandled exception was generated during the execution of the
current web request. Information regarding the origin and location of
the exception can be identified using the exception stack trace below.
Stack Trace:
[TypeLoadException: Could not load type
'System.Runtime.CompilerServices.ExtensionAttribute' from assembly
'mscorlib, Version=4.0.0.0, Culture=neutral,
PublicKeyToken=b77a5c561934e089'.]
System.ModuleHandle.ResolveType(RuntimeModule module, Int32 typeToken,
IntPtr* typeInstArgs, Int32 typeInstCount, IntPtr* methodInstArgs,
Int32 methodInstCount, ObjectHandleOnStack type) +0
System.ModuleHandle.ResolveTypeHandleInternal(RuntimeModule module,
Int32 typeToken, RuntimeTypeHandle[] typeInstantiationContext,
RuntimeTypeHandle[] methodInstantiationContext) +525
System.ModuleHandle.ResolveTypeHandle(Int32 typeToken,
RuntimeTypeHandle[] typeInstantiationContext, RuntimeTypeHandle[]
methodInstantiationContext) +19
System.Reflection.RuntimeModule.ResolveType(Int32 metadataToken,
Type[] genericTypeArguments, Type[] genericMethodArguments) +315
System.Reflection.CustomAttribute.FilterCustomAttributeRecord(CustomAttributeRecord
caRecord, MetadataImport scope, Assembly& lastAptcaOkAssembly,
RuntimeModule decoratedModule, MetadataToken decoratedToken,
RuntimeType attributeFilterType, Boolean mustBeInheritable, Object[]
attributes, IList derivedAttributes, RuntimeType& attributeType,
IRuntimeMethodInfo& ctor, Boolean& ctorHasParameters, Boolean&
isVarArg) +208
System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeModule
decoratedModule, Int32 decoratedMetadataToken, Int32 pcaCount,
RuntimeType attributeFilterType, Boolean mustBeInheritable, IList
derivedAttributes, Boolean isDecoratedTargetSecurityTransparent) +1171
System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeAssembly
assembly, RuntimeType caType) +146
WebActivator.AssemblyExtensions.GetActivationAttributes(Assembly
assembly) +114
WebActivator.ActivationManager.RunActivationMethods() +286
WebActivator.ActivationManager.RunPreStartMethods() +38
WebActivator.ActivationManager.Run() +56
[InvalidOperationException: The pre-application start initialization
method Run on type WebActivator.ActivationManager threw an exception
with the following error message: Could not load type
'System.Runtime.CompilerServices.ExtensionAttribute' from assembly
'mscorlib, Version=4.0.0.0, Culture=neutral,
PublicKeyToken=b77a5c561934e089'..]
System.Web.Compilation.BuildManager.InvokePreStartInitMethods(ICollection`1
methods) [phone]
System.Web.Compilation.BuildManager.CallPreStartInitMethods() +465
System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager
appManager, IApplicationHost appHost, IConfigMapPathFactory
configMapPathFactory, HostingEnvironmentParameters hostingParameters,
PolicyLevel policyLevel, Exception appDomainCreationException) +1167
[HttpException (0x80004005): The pre-application start initialization
method Run on type WebActivator.ActivationManager threw an exception
with the following error message: Could not load type
'System.Runtime.CompilerServices.ExtensionAttribute' from assembly
'mscorlib, Version=4.0.0.0, Culture=neutral,
PublicKeyToken=b77a5c561934e089'..]
System.Web.HttpRuntime.FirstRequestInit(HttpContext context) [phone]
System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context)
+141 System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest
wr, HttpContext context) +4813333
None of my searching has turned up anything terribly helpful, but the main avenue I've explored is a potential conflict between the version of .NET that Ninject was built against and the version that I'm actually running. I've never installed .NET 4.5 on my system, so I'm certain that I'm building against 4.0. I then built the most recent version of Ninject (3.0.2) and the extensions from source to be sure that it's using 4.0 as well. I also tried adding all the libraries that I'm using in the real app to my test app to see if there's a conflict but that didn't turn up anything. (However, I didn't go so far as to put in code that exercises them. I don't know if that would change anything.)
Has anyone seen this kind of problem before or have any ideas that I can try? Is there more info I can provide that would be helpful?
Alternatively, is there some other way I can use Ninject in an ASP.NET application instead of the ninject.web extension? Would wrapping the Ninject kernel up in a singleton work just as well?