I have upgraded DNN 6 to DNN 7.0.6 my site. But now I am getting following error for all admin and host pages. Also for some settings pages in the modules.

Host Settings
Error: Host Settings is currently unavailable. DotNetNuke.Services.Exceptions.ModuleLoadException: External component has thrown an exception. ---> System.Web.HttpCompileException: External component has thrown an exception. at System.Web.Compilation.AssemblyBuilder.Compile() at System.Web.Compilation.BuildProvidersCompiler.PerformBuild() at System.Web.Compilation.BuildManager.CompileWebFile(VirtualPath virtualPath) at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate) at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate) at System.Web.UI.TemplateControl.LoadControl(VirtualPath virtualPath) at DotNetNuke.UI.ControlUtilities.LoadControl[T](TemplateControl containerControl, String ControlSrc) at DotNetNuke.UI.Modules.WebFormsModuleControlFactory.CreateModuleControl(TemplateControl containerControl, ModuleInfo moduleConfiguration) at DotNetNuke.UI.Modules.ModuleControlFactory.LoadModuleControl(TemplateControl containerControl, ModuleInfo moduleConfiguration) at DotNetNuke.UI.Modules.ModuleHost.LoadModuleControl() --- End of inner exception stack trace ---

Where could be the issue? What would be the solution? I have seen this issue for other people as well. But no good answer yet.

The issue has started from DNN 7.X.X versions.

Please help! Thanks you!