When I try to add a new xslt file via umbraco back end, I get the following error.

If I just add the file and create a macro and reference it, then the page with the macro will put out the same error.

Server Error in '/' Application.
Unable to load one or more of the types in assembly 'Microsoft.Practices.EnterpriseLibrary.Caching, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'. Exceptions were thrown:
System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.Practices.Unity, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.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.Exception: Unable to load one or more of the types in assembly 'Microsoft.Practices.EnterpriseLibrary.Caching, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'. Exceptions were thrown:
System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.Practices.Unity, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

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: 

[Exception: Unable to load one or more of the types in assembly 'Microsoft.Practices.EnterpriseLibrary.Caching, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'. Exceptions were thrown:
System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.Practices.Unity, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.]
   umbraco.BusinessLogic.Utils.TypeFinder.FindClassesMarkedWithAttribute(Assembly assembly, Type attribute) +309
   umbraco.BusinessLogic.Utils.TypeFinder.FindClassesMarkedWithAttribute(Type attribute) +124
   umbraco.macro.GetXsltExtensionsImpl() +884
   umbraco.macro.<GetXsltExtensions>b__4() +5
   umbraco.cms.businesslogic.cache.Cache.GetCacheItem(String cacheKey, Object syncLock, CacheItemPriority priority, CacheItemRemovedCallback refreshAction, CacheDependency cacheDependency, TimeSpan timeout, GetCacheItemDelegate`1 getCacheItem) +132
   umbraco.macro.GetXsltExtensions() +215
   umbraco.macro.AddXsltExtensionsToHeader(String xslt) +131
   umbraco.XsltTasks.Save() +412
   umbraco.presentation.create.dialogHandler_temp.Create(String NodeType, Int32 TypeId, Int32 NodeId, String Text) +385
   umbraco.presentation.create.xslt.sbmt_Click(Object sender, EventArgs e) +174
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +118
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +112
   System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +5563








Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.272

I have read some similar threads (http://our.umbraco.org/forum/developers/xslt/27131-Cannot-add-or-save-XSLT-file-due-to-missing-SystemWebMVC-reference) but haven't found a solution.

Microsoft.Practices.EnterpriseLibrary.Caching.dll is in the bin directory and it is in the references for the project.

Other developers working on this project (obviously on a different machine) do not have this problem.

I am working in VS2010.  Another umbraco project I have in vs2010 gives me the same error, however a site I work on in vs2008 does not.  So something I guess in my setup, but I have no idea what!

Any help welcome please because I am stumped!