If you are experiencing weird errors in asp.net mvc.
You have added namespace in Web.config file still your View Page is not reflecting any change or still control is error-ed out, then close the view and reopen it. Yes VS.Net requires closing and opening of view page in order to reflect changes.
You have made major change in Entity Framework (Code First) Entity class and even though making sure that all changes are properly applied if you receive any runtime error saying "Invalid column name" or may be something as shown below: Then simply close your asp.net mvc project (VS.Net Solution) and open it again. (Yes i found this weird because it requires me to close my vs.net solution and reopen it again to reflect all changes, even though i tried clean solution and rebuild solution before running project)
at System.Data.EntityClient.EntityCommandDefinition.ExecuteStoreCommands(EntityCommand entityCommand, CommandBehavior behavior)
at System.Data.Objects.Internal.ObjectQueryExecutionPlan.Execute[TResultType](ObjectContext context, ObjectParameterCollection parameterValues)
at System.Data.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at MyBlog.Controllers.StepbystepController.Index() in d:\Websites\Source\MyBlog\MyBlog\Controllers\StepbystepController.cs:line 27
at lambda_method(Closure , ControllerBase , Object )
at System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object parameters)
at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult)
You have change model in view then to apply changes you need to close view and reopen it again.
Now below situation are something becoz of our mistake but we don't generally noticed. Mostly this errors result in 404 - Error Page.
If you are getting 404 Error in asp.net mvc then make sure
1) Check action name and then check view name.
Example: You have created "ContactMessage" action method in Home controller and you have created "Contact" view page, this mismatch will result in 404 error. I know you new this but you don't realize this when 404 occurs.
2) Check whether you have created view page under correct directory name. I will not go deep into Asp.net MVC Hierarchy structure but as you know that proper naming convention needs to follow, so by mistake if you have created view under wrong directory that will also results in 404 error page.
3) Check whether controls on your view is not error-ed out. (They are getting proper values assigned from model).
4) You can always turn CustomErrors mode="RemoteOnly" to simply attack problem at first.
There are few other situations but i can't able to recall them all, but you get the gist of my post.
Moral of story: All errors mentioned here are either becoz of our mistake or vs.net, but we don't generally noticed, so if you run into similar situation then answer is relax and try to make sure that things are not becoz of your mistake before jumping into find solution.