Could not load file or assembly error in ASP.NET when IIS server is idle

I am using ASP.NET MVC technology to create a website. The site is hosted on IIS 7 server. If the site is not accessed for a while i get the "Could not load file or assembly error " . The error disappears after a single page refresh. I know the DLL is formed as part of project structure automatically by Asp.Net MVC Model. FS is the projects name

The complete error is below.

A web search did not produce a permanent solution to this problem. It would be great If any one has some fix for this issue.

Thanks in advance.

Could not load file or assembly 'FS, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. HTTP download of assemblies has been disabled for this appdomain. (Exception from HRESULT: 0x80131048) 
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.IO.FileLoadException: Could not load file or assembly 'FS, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. HTTP download of assemblies has been disabled for this appdomain. (Exception from HRESULT: 0x80131048) 
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:  

[FileLoadException: Could not load file or assembly 'FS, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. HTTP download of assemblies has been disabled for this appdomain. (Exception from HRESULT: 0x80131048)]
   System.Reflection.Assembly._GetType(String name, Boolean throwOnError, Boolean ignoreCase) +0
   System.Reflection.Assembly.GetType(String name) +25
   System.Web.Compilation.BaseTemplateBuildProvider.GetGeneratedType(CompilerResults results) +55
   System.Web.Compilation.BuildProvider.CreateBuildResult(CompilerResults results) +45
   System.Web.Compilation.BuildProvider.GetBuildResult(CompilerResults results) +13
   System.Web.Compilation.ApplicationBuildProvider.GetGlobalAsaxBuildResult(Boolean isPrecompiledApp) +275
   System.Web.Compilation.BuildManager.CompileGlobalAsax() +52
   System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +337 
[HttpException (0x80004005): Could not load file or assembly 'FS, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. HTTP download of assemblies has been disabled for this appdomain. (Exception from HRESULT: 0x80131048)]
   System.Web.Compilation.BuildManager.ReportTopLevelCompilationException() +58
   System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +512
   System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters) +729 
[HttpException (0x80004005): Could not load file or assembly 'FS, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. HTTP download of assemblies has been disabled for this appdomain. (Exception from HRESULT: 0x80131048)]
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +8890735
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +85
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +333