Debugging .NET Framework and MS Visual Studio Managed Classes at Run time and Design time

I found this article on askjeeves.com and was looking for others who
successfully got this to work. I am trying to debug though system.web but
when i use a compiled system.web with debugging info i get the below error.

http://www.codeproject.com/dotnet/De...rk_Classes.asp

Server Error in '/Whatzupv5' Application.
--------------------------------------------------------------------------------

Could not load type System.Web.Caching.ExpiresEntry from assembly
System.Web, Version=1.0.5000.0, Culture=neutral,
PublicKeyToken=b03f5f7f11d50a3a.
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.Web.Caching.ExpiresEntry from assembly System.Web,
Version=1.0.5000.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a.

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.Web.Caching.ExpiresEntry from
assembly System.Web, Version=1.0.5000.0, Culture=neutral,
PublicKeyToken=b03f5f7f11d50a3a.]
System.Web.Caching.ExpiresBucket.AddCacheEntry(CacheEntry cacheEntry) +0
System.Web.Caching.CacheExpires.Add(CacheEntry cacheEntry)
System.Web.Caching.CacheSingle.UpdateCache(CacheKey cacheKey, CacheEntry
newEntry, Boolean replace, CacheItemRemovedReason removedReason, Object&
valueOld)
System.Web.Caching.CacheInternal.DoInsert(Boolean isPublic, String key,
Object value, CacheDependency dependencies, DateTime utcAbsoluteExpiration,
TimeSpan slidingExpiration, CacheItemPriority priority,
CacheItemRemovedCallback onRemoveCallback, Boolean replace)
System.Web.Caching.CacheInternal.UtcInsert(String key, Object value,
CacheDependency dependencies, DateTime utcAbsoluteExpiration, TimeSpan
slidingExpiration)
System.Web.Hosting.ISAPIWorkerRequest.MapPath(String path)
System.Web.Configuration.HttpConfigurationSystem.Init(HttpContext context)
System.Web.HttpRuntime.InitConfiguration(HttpContext context)
System.Web.HttpRuntime.FirstRequestInit(HttpContext context)

[HttpException (0x80004005): ASP.NET Initialization Error]
System.Web.HttpRuntime.FirstRequestInit(HttpContext context)
System.Web.HttpRuntime.ProcessRequestInternal(HttpWorkerRequest wr)