'Microsoft.TeamFoundation.WorkItemTracking.Client.DataStoreLoader' or one of its dependencies can not be loaded

Exception information:

    Exception type: ConfigurationErrorsException

    Exception message: Could not load file or assembly 'Microsoft.TeamFoundation.WorkItemTracking.Client.DataStoreLoader' or one of its dependencies. An attempt was made to load a program with an incorrect format.

   at System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective)

   at System.Web.Configuration.CompilationSection.LoadAllAssembliesFromAppDomainBinDirectory()

   at System.Web.Configuration.AssemblyInfo.get_AssemblyInternal()

   at System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig)

   at System.Web.Compilation.BuildManager.CallPreStartInitMethods()

   at System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException)

Could not load file or assembly 'Microsoft.TeamFoundation.WorkItemTracking.Client.DataStoreLoader' or one of its dependencies. An attempt was made to load a program with an incorrect format.

   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.Reflection.Assembly.Load(String assemblyString)

   at System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective)

Object Model being used v11.0.50727.1

Microsoft.TeamFoundation.dll
Microsoft.TeamFoundation.Client.dll
Microsoft.TeamFoundation.Common.dll
Microsoft.TeamFoundation.WorkItemTracking.Client.dll
Microsoft.TeamFoundation.WorkItemTracking.Common.dll

Then when compiled the following dlls are being pulled in Indirectly
Microsoft.TeamFoundation.WorkItemTracking.Client.DataStoreLoader.dll
Microsoft.WITDataStore.dll

Fusion Log
WRN: Partial binding information was supplied for an assembly:
WRN: Assembly Name: Microsoft.TeamFoundation.WorkItemTracking.Client.DataStoreLoader | Domain ID: 4
WRN: A partial bind occurs when only part of the assembly display name is provided.
WRN: This might result in the binder loading an incorrect assembly.
WRN: It is recommended to provide a fully specified textual identity for the assembly,
WRN: that consists of the simple name, version, culture, and public key token.
WRN: See whitepaper http://go.microsoft.com/fwlink/?LinkId=109270 for more information and common solutions to this issue.
LOG: Appbase = file:///D:/WebSites/buildRequest/
LOG: Initial PrivatePath = D:\WebSites\buildRequest\bin
Calling assembly : (Unknown).
===
LOG: This bind starts in default load context.
LOG: Using application configuration file: D:\WebSites\buildRequest\web.config
LOG: Using host configuration file: C:\Windows\Microsoft.NET\Framework64\v4.0.30319\aspnet.config
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework64\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/Framework64/v4.0.30319/Temporary ASP.NET Files/buildrequest/63419838/daacaf55/Microsoft.TeamFoundation.WorkItemTracking.Client.DataStoreLoader.DLL.
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework64/v4.0.30319/Temporary ASP.NET Files/buildrequest/63419838/daacaf55/Microsoft.TeamFoundation.WorkItemTracking.Client.DataStoreLoader/Microsoft.TeamFoundation.WorkItemTracking.Client.DataStoreLoader.DLL.
LOG: Attempting download of new URL file:///D:/WebSites/buildRequest/bin/Microsoft.TeamFoundation.WorkItemTracking.Client.DataStoreLoader.DLL.
ERR: Failed to complete setup of assembly (hr = 0x8007000b). Probing terminated.

any pointers appreciated.

Ryan