VS2010 Strange ASP.NET Startup Errors

[Zempersfa]

I have existing VS2010 ASP.NET solution which was working OK. However now when I try to run it, I get some very strange (seemingly random combination of) errors:

• Invalid file name for file monitoring: '[Web App Path]\Controls' (this is a directory)
• Requested registry access is not allowed. (Source: mscorlib - the call Stack says its parent higher up the stack is from System.Web.Compliation.BuildManager.ExecutePreAppStart())
• System.Web.HttpException occurred / HResult=-2147467259 / Message=File does not exist.
• Access to the path: 'C:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\root\6c9c2bea\84b35c9c\App_Web_cyfzelmo.dll' is denied. (also App_Browsers.dvwnc2tw.dll, App_global.asax.wtigsdou.dll)
• An existing connection was forcibly closed by the remote host
• Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED)) - System.Threading.Monitor.ReliableEnter(Object obj, Boolean& lockTaken)at System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context)
• Value cannot be null. Parameter name: source [stack parent: System.Web.Compilation.BuildManager.LoadCachedPreAppStartAssemblies(string preStartInitListPath)]

These are only shown if I have Debug/Exceptions/CLR Exceptions (Thrown) set, however I don't recall seeing them before (I usually always have this option set). I created a blank ASP.NET solution, enabled CLR Exceptions (Thrown) and also got the registry and argument null error - whenever I rebuilt and re-ran the solution.I have recently installed VS2012 as well, but am not sure if this is a cause. I've also upgraded my Telerik controls - but my blank solution doesn't have them configured.I think I'll try a repair install of VS2010 just to see if this fixes it.