Unable to migrate from Unity 2.0 to Unity 2.1.505.0

Unable to migrate from Unity 2.0 to Unity 2.1.505.0

I have an application written using Unity 2.0 and I am trying to migrate
to version 2.1.505.0. I changed the reference in the project to point to
the DLL corresponding to the newer version. When I build the solution, it
goes through fine. However, when I try to run the application, it gives me
a FileNotfoundException:
Stack Trace:
[FileLoadException: Could not load file or assembly
'Microsoft.Practices.Unity, Version=2.0.414.0, Culture=neutral,
PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located
assembly's manifest definition does not match the assembly reference.
(Exception from HRESULT: 0x80131040)]
InsightsService.WebApi.WebApiApplication.Application_Start() in
E:\tfs\DisplayApps\Services\InsightsBps\Dev\source\InsightsService.WebApi\Global.asax.cs:30
[HttpException (0x80004005): Could not load file or assembly
'Microsoft.Practices.Unity, Version=2.0.414.0, Culture=neutral,
PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located
assembly's manifest definition does not match the assembly reference.
(Exception from HRESULT: 0x80131040)]
System.Web.HttpApplicationFactory.EnsureAppStartCalledForIntegratedMode(HttpContext
context, HttpApplication app) +12863325
System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr
appContext, HttpContext context, MethodInfo[] handlers) +175
System.Web.HttpApplication.InitSpecial(HttpApplicationState state,
MethodInfo[] handlers, IntPtr appContext, HttpContext context) +304
System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr
appContext, HttpContext context) +404
System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr
appContext) +475
[HttpException (0x80004005): Could not load file or assembly
'Microsoft.Practices.Unity, Version=2.0.414.0, Culture=neutral,
PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located
assembly's manifest definition does not match the assembly reference.
(Exception from HRESULT: 0x80131040)]
System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +12880068
System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +159
System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest
wr, HttpContext context) +12721257
I checked web.config and cold not find any overrides. I even cleaned the
solution and rebuilt it, but the problem persists. What could be wrong
here?